denial-of-service open threat signaling (dots). · architecture, called ddos open threat signaling...

Network Working Group M. BoucadairInternet-Draft OrangeIntended status: Standards Track T. ReddyExpires: January 1, 2018 McAfee June 30, 2017

Multi-homing Considerations for Distributed-Denial-of-Service Open Threat Signaling (DOTS) draft-boucadair-dots-multihoming-01

Abstract

This document discusses multi-homing considerations for Distributed- Denial-of-Service Open Threat Signaling (DOTS).

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on January 1, 2018.

Copyright Notice

Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust’s Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of

Boucadair & Reddy Expires January 1, 2018 []

Internet-Draft DOTS Multihoming June 2017

publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Multi-Homing Scenarios . . . . . . . . . . . . . . . . . . . 3 3.1. Residential CPE . . . . . . . . . . . . . . . . . . . . . 4 3.2. Multi-homed Enterprise: Single CPE, Multiple Upstream ISPs . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.3. Multi-homed Enterprise: Multiple CPEs, Multiple Upstream ISPs . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.4. Multi-homed Enterprise with the Same ISP . . . . . . . . 6 4. DOTS Deployment Considerations . . . . . . . . . . . . . . . 6 4.1. Residential CPE . . . . . . . . . . . . . . . . . . . . . 7 4.2. Multi-homed Enterprise: Single CPE, Multiple Upstream ISPs . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.3. Multi-homed Enterprise: Multiple CPEs, Multiple Upstream ISPs . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.4. Multi-homed Enterprise: Single ISP . . . . . . . . . . . 11 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 8.1. Normative References . . . . . . . . . . . . . . . . . . 12 8.2. Informative References . . . . . . . . . . . . . . . . . 12 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 13

1. Introduction

In many deployments, it may not be possible for a network to determine the cause for a distributed Denial-of-Service (DoS) attack [RFC4732], but instead just realize that some resources seem to be under attack. To fill that gap, the IETF is specifying an architecture, called DDoS Open Threat Signaling (DOTS) [I-D.ietf-dots-architecture], in which a DOTS client can inform a DOTS server that the network is under a potential attack and that appropriate mitigation actions are required. Indeed, because the lack of a common method to coordinate a real-time response among involved actors and network domains inhibits the effectiveness of DDoS attack mitigation, DOTS protocol is meant to carry requests for DDoS attack mitigation, thereby reducing the impact of an attack and leading to more efficient defensive actions.



[I-D.ietf-dots-use-cases] identifies a set of scenarios for DOTS; almost all these scenarios involve a CPE.

The basic high-level DOTS architecture is illustrated in Figure 1 ([I-D.ietf-dots-architecture]):

+-----------+ +-------------+ | Mitigator | ˜˜˜˜˜˜˜˜˜˜ | DOTS Server | +-----------+ +-------------+ | | | +---------------+ +-------------+ | Attack Target | ˜˜˜˜˜˜ | DOTS Client | +---------------+ +-------------+

Figure 1: Basic DOTS Architecture

[I-D.ietf-dots-architecture] specifies that the DOTS client may be provided with a list of DOTS servers; each associated with one or more IP addresses. These addresses may or may not be of the same address family. The DOTS client establishes one or more DOTS signaling sessions by connecting to the provided DOTS server(s) addresses.

DOTS may be deployed within networks that are connected to one single upstream provider. It can also be enabled within networks that are multi-homed. The reader may refer to [RFC3582] for an overview of multi-homing goals and motivations. This document discusses DOTS multi-homing considerations.

2. Terminology

This document makes use of the terms defined in [I-D.ietf-dots-architecture] and [RFC4116].

IP refers to both IPv4 and IPv6.

3. Multi-Homing Scenarios

This section briefly describes some multi-homing scenarios that are relevant to DOTS. In the following sub-sections, only the connections of border routers are shown; internal network topologies are not elaborated hereafter.



3.1. Residential CPE

The scenario shown in Figure 2 is characterized as follows:

o The home network is connected to the Internet using one single CPE (Customer Premises Equipment).

o The CPE is connected to multiple provisioning domains (i.e. both fixed and mobile networks). Provisioning domain (PvD) is explained in [RFC7556].

o Each of these provisioning domains assign IP addresses/prefixes to the CPE. These addresses/prefixes are said to be Provider- Aggregatable (PA).

o The CPE is provided by each of these provisioning domains with additional configuration information such as a list of DNS servers, DNS suffixes associated with the network, default gateway address, and DOTS server’s name [I-D.boucadair-dots-server-discovery].

o Because of ingress filtering, packets forwarded by the CPE to a given provisioning domain must be send with a source IP address that was assigned by that network [RFC8043].

+-------+ +-------+ |Fixed | |Mobile | |Network| |Network| +---+---+ +---+---+ | | Service Providers ............|....................|....................... +---------++---------+ Home Network || +--++-+ | CPE | +-----+ ... (Internal Network)

Figure 2: Typical Multi-homed Residential CPE

3.2. Multi-homed Enterprise: Single CPE, Multiple Upstream ISPs


o The enterprise network is connected to the Internet using one single router.



o That router is connected to multiple provisioning domains (i.e. managed by distinct administrative entities).

Unlike the previous scenario, two sub-cases can be considered for an enterprise network with regards to assigned addresses:

1. Provider Independent (PI) addresses: The enterprise is the owner of the IP addresses/prefixes; the same address/prefix is then used for communication placed using any of the provisioning domains.

2. PA addresses/prefixes: each of provisioning domains assigns IP addresses/prefixes to the enterprise network.

+------+ +------+ | ISP1 | | ISP2 | +---+--+ +--+---+ | | Service Providers ............|....................|....................... +---------++---------+ Enterprise Network || +--++-+ | rtr | +-----+ ... (Internal Network)

Figure 3: Multi-homed Enterprise Network (Single CPE connected to Multiple Networks)

3.3. Multi-homed Enterprise: Multiple CPEs, Multiple Upstream ISPs

This scenario is similar to the one in Section 3.2; the main difference is that dedicated routers are used to connect to each provisioning domain.



These deployment schemes are further discussed in the following sub- sections.


Figure 5 depicts DOTS signaling sessions that are required to be established between a DOTS client (C) and DOTS servers (S1, S2) in the context of the scenario described in Section 3.1.

The DOTS client MUST resolve the DOTS server’s name provided by a provisioning domain ([I-D.boucadair-dots-server-discovery]) using the DNS servers learned from the same provisioning domain. The DOTS client MUST use the source address selection algorithm defined in [RFC6724] to select the candidate source addresses to contact each of these DOTS servers. DOTS signaling sessions must be established and maintained with each of the DOTS servers because the mitigation scope of these servers is restricted. The DOTS client SHOULD use the certificate provisioned by a provisioning domain to authenticate itself to the DOTS server provided by the same provisioning domain. When conveying a mitigation request to protect the attack target(s), the DOTS client among the DOTS servers available MUST select a DOTS server whose network has assigned the prefixes from which target prefixes and target IP addresses are derived. For example, mitigation request to protect target resources bound to a PA IP address/prefix cannot be honored by an provisioning domain other than the one that owns those addresses/prefixes. Consequently, Typically, if a CPE detects a DDoS attack on all its network attachments, it must contact both DOTS servers for mitigation. Nevertheless, if the DDoS attack is received from one single network, then only the DOTS server of that network must be contacted.

The DOTS client MUST be able to associate a DOTS server with each provisioning domain. For example, if the DOTS client is provisioned with S1 using DHCP when attaching to a first network and with S2 using Protocol Configuration Option (PCO) when attaching to a second network, the DOTS client must record the interface from which a DOTS server was provisioned. DOTS signaling session to a given DOTS server must be established using the interface from which the DOTS server was provisioned.



+--+ -----------|S1| / +--+ / / +---+/ | C | +---+\ \ \ \ +--+ -----------|S2| +--+

Figure 5: DOTS associations for a multihomed residential CPE


Figure 6 illustrates a first set of DOTS associations that can be established with a DOTS gateway is enabled in the context of the scenario described in Section 3.2. This deployment is characterized as follows:

o One of more DOTS clients are enabled in hosts located in the internal network.

o A DOTS getaway is enabled to aggregate/relay the requests to upstream DOTS servers.

When PA addresses/prefixes are in used, the same considerations discussed in Section 4.1 are to be followed by the DOTS gateway to contact its DOTS server(s). The DOTS gateways can be reachable from DOTS client using a unicast or anycast address.

Nevertheless, when PI addresses/prefixes are assigned, the DOTS gateway MUST sent the same request to all its DOTS servers.



+--+ -----------|S1| +---+ / +--+ | C1|----+ / +---+ | / +---+ +-+-+/ | C3|------| G | +---+ +-+-+\ +---+ | \ | C2|----+ \ +---+ \ +--+ -----------|S2| +--+

Figure 6: Multiple DOTS Clients, Single DOTS Gateway, Multiple DOTS Servers

An alternate deployment model is depicted in Figure 7. This deployment assumes that:

o One of more DOTS clients are enabled in hosts located in the internal network. These DOTS client may use [I-D.boucadair-dots-server-discovery] to discover its DOTS server(s).

o These DOTS clients communicate directly with upstream DOTS servers.

If PI addresses/prefixes are in use, the DOTS client can send the mitigation request for all its PI addresses/prefixes to any one of the DOTS servers. The use of anycast addresses is NOT RECOMMENDED.

If PA addresses/prefxies are used, the same considerations discussed in Section 4.1 are to be followed by the DOTS clients. Because DOTS clients are not located on the CPE and multiple addreses/prefixes may not be assigned to the DOTS client (IPv4 context, typically), some complications arise to steer the traffic to the appropriate DOTS server using the appropriate source IP address. These complications discussed in [RFC4116] are not specific to DOTS .



+--+ +--------|C1|--------+ | +--+ | +--+ +--+ +--+ |S2|------|C3|------|S1| +--+ +--+ +--+ | +--+ | +--------|C2|--------+ +--+

Figure 7: Multiple DOTS Clients, Multiple DOTS Servers

Another deployment approach is to enable many DOTS clients; each of them responsible to handle communication with a specific DOTS server (see Figure 8). Each DOTS client is provided with policies (e.g., prefix filter) that will trigger DOTS communications with the DOTS servers. The CPE MUST select the appropriate source IP address when forwarding DOTS messages received from an internal DOTS client. If anycast addresses are used to reach DOTS servers, the CPE may not be able to select the appropriate provisioning domain to which the mitigation request should be forwarded. As a consequence, the request may not be forwarded to the appropriate DOTS server.

+--+ +--------|C1| | +--+ +--+ +--+ +--+ |S2| |C2|------|S1| +--+ +--+ +--+

Figure 8: Single Homed DOTS Clients


The deployments depicted in Figure 7 and Figure 8 apply also for the scenario described in Section 3.3. One specific problem for this scenario is to select the appropriate exit router when contacting a given DOTS server.

An alternative deployment scheme is shown in Figure 9:

o DOTS clients are enabled in hosts located in the internal network.

o A DOTS gateway is enabled in each CPE (rtr1, rtr2).

o Each of these DOTS gateways communicate with the DOTS server of the provisioning domain.



When PI addresses/prefixes are used, DOTS clients can contact any of the DOTS gateways to send a DOTS message. DOTS gateway will then relay the request to the DOTS server. Note that the use of anycast addresses is NOT RECOMMENDED to establish DOTS signaling sessions between DOTS client and DOTS gateways.

When PA addresses/prefixes are used, but no filter rules are provided to DOTS clients, these later MUST contact all DOTS gateways simultaneously to send a DOTS message. Upon receipt of a request by a DOTS gateway, it MUST check whether the request is to be forwarded upstream or be rejected.

When PA addresses/prefixes are used, but specific filter rules are provided to DOTS clients using some means that are out of scope, these later MUST select the appropriate DOTS gateway to be contacted. The use of anycast is NOT RECOMMENDED to reach DOTS gateways.

+---+ +------------| C1|----+ | +---+ | +--+ +-+-+ +---+ +-+-+ +--+ |S2|------|G2 |------| C3|------|G1 |------|S1| +--+ +-+-+ +---+ +-+-+ +--+ | +---+ | +------------| C2|----+ +---+

Figure 9: Multiple DOTS Clients, Multiple DOTS Gateways, Multiple DOTS Servers

4.4. Multi-homed Enterprise: Single ISP

The key difference of the scenario described in Section 3.4 compared to the other scenarios is that multi-homing is provided by the same ISP. Concretely, that ISP can decided to provision the enterprise network with:

1. The same DOTS server for all network attachments.

2. Distinct DOTS servers for each network attachment. These DOTS servers needs to coordinate when a mitigation action is received from the enterprise network.

In both cases, DOTS agents enabled within the enterprise network may decide to select one or all network attachments to place DOTS mitigation requests.



5. Security Considerations

DOTS-related security considerations are discussed in Section 4 of [I-D.ietf-dots-architecture].

TBD: In Home networks, if EST is used then how will the DOTS gateway (EST client) be provisioned with credentials for initial enrolment (see Section 2.2 in RFC 7030).

6. IANA Considerations

This document does not require any action from IANA.

7. Acknowledgements

To be completed.

8. References

8.1. Normative References

[I-D.ietf-dots-architecture] Mortensen, A., Andreasen, F., Reddy, T., [email protected], c., Compton, R., and N. Teague, "Distributed-Denial-of-Service Open Threat Signaling (DOTS) Architecture", draft-ietf-dots- architecture-03 (work in progress), June 2017.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>.

[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown, "Default Address Selection for Internet Protocol Version 6 (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012, <http://www.rfc-editor.org/info/rfc6724>.

8.2. Informative References

[I-D.boucadair-dots-server-discovery] Boucadair, M., Reddy, T., and P. Patil, "Distributed- Denial-of-Service Open Threat Signaling (DOTS) Server Discovery", draft-boucadair-dots-server-discovery-00 (work in progress), June 2017.



[I-D.ietf-dots-use-cases] Dobbins, R., Fouant, S., Migault, D., Moskowitz, R., Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS Open Threat Signaling (DDoS) Open Threat Signaling", draft-ietf-dots-use-cases-05 (work in progress), May 2017.

[RFC3582] Abley, J., Black, B., and V. Gill, "Goals for IPv6 Site- Multihoming Architectures", RFC 3582, DOI 10.17487/RFC3582, August 2003, <http://www.rfc-editor.org/info/rfc3582>.

[RFC4116] Abley, J., Lindqvist, K., Davies, E., Black, B., and V. Gill, "IPv4 Multihoming Practices and Limitations", RFC 4116, DOI 10.17487/RFC4116, July 2005, <http://www.rfc-editor.org/info/rfc4116>.

[RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet Denial-of-Service Considerations", RFC 4732, DOI 10.17487/RFC4732, December 2006, <http://www.rfc-editor.org/info/rfc4732>.

[RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015, <http://www.rfc-editor.org/info/rfc7556>.

[RFC8043] Sarikaya, B. and M. Boucadair, "Source-Address-Dependent Routing and Source Address Selection for IPv6 Hosts: Overview of the Problem Space", RFC 8043, DOI 10.17487/RFC8043, January 2017, <http://www.rfc-editor.org/info/rfc8043>.

Authors’ Addresses

Mohamed Boucadair Orange Rennes 35000 France

Email: [email protected]

Tirumaleswar Reddy McAfee, Inc. Embassy Golf Link Business Park Bangalore, Karnataka 560071 India



Network Working Group M. BoucadairInternet-Draft OrangeIntended status: Standards Track T. ReddyExpires: April 10, 2019 McAfee October 7, 2018

Multi-homing Deployment Considerations for Distributed-Denial-of-Service Open Threat Signaling (DOTS) draft-boucadair-dots-multihoming-04

Abstract

This document discusses multi-homing considerations for Distributed- Denial-of-Service Open Threat Signaling (DOTS). The goal is to provide a set of guidance for DOTS clients/gateways when multihomed.

Status of This Memo


Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/.


This Internet-Draft will expire on April 10, 2019.

Copyright Notice


This document is subject to BCP 78 and the IETF Trust’s Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Boucadair & Reddy Expires April 10, 2019 [Page 1]

Internet-Draft DOTS Multihoming October 2018

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Multi-Homing Scenarios . . . . . . . . . . . . . . . . . . . 4 4.1. Residential CPE . . . . . . . . . . . . . . . . . . . . . 4 4.2. Multi-homed Enterprise: Single CPE, Multiple Upstream ISPs . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.3. Multi-homed Enterprise: Multiple CPEs, Multiple Upstream ISPs . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.4. Multi-homed Enterprise with the Same ISP . . . . . . . . 7 5. DOTS Deployment Considerations . . . . . . . . . . . . . . . 7 5.1. Residential CPE . . . . . . . . . . . . . . . . . . . . . 7 5.2. Multi-homed Enterprise: Single CPE, Multiple Upstream ISPs . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.3. Multi-homed Enterprise: Multiple CPEs, Multiple Upstream ISPs . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.4. Multi-homed Enterprise: Single ISP . . . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 9.1. Normative References . . . . . . . . . . . . . . . . . . 12 9.2. Informative References . . . . . . . . . . . . . . . . . 13 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 14

1. Introduction

In many deployments, it may not be possible for a network to determine the cause for a distributed Denial-of-Service (DoS) attack [RFC4732], but instead just realize that some resources seem to be under attack. To fill that gap, the IETF is specifying an architecture, called DDoS Open Threat Signaling (DOTS) [I-D.ietf-dots-architecture], in which a DOTS client can inform a DOTS server that the network is under a potential attack and that appropriate mitigation actions are required. Indeed, because the lack of a common method to coordinate a real-time response among involved actors and network domains inhibits the effectiveness of DDoS attack mitigation, DOTS protocol is meant to carry requests for DDoS attack mitigation, thereby reducing the impact of an attack and leading to more efficient defensive actions. [I-D.ietf-dots-use-cases] identifies a set of scenarios for DOTS; almost all these scenarios involve a CPE.






[I-D.ietf-dots-architecture] specifies that the DOTS client may be provided with a list of DOTS servers; each associated with one or more IP addresses. These addresses may or may not be of the same address family. The DOTS client establishes one or more DOTS signaling sessions by connecting to the provided DOTS server(s) addresses.

DOTS may be deployed within networks that are connected to one single upstream provider. It can also be enabled within networks that are multi-homed. The reader may refer to [RFC3582] for an overview of multi-homing goals and motivations. This document discusses DOTS multi-homing considerations. Specifically, the document aims to:

1. Complete the base DOTS architecture with multi-homing specifics. Those specifics need to be taking into account because:

* Send a DOTS mitigation request to an arbitrary DOTS server won’t help mitigating a DDoS attack.

* Blindly forking all DOTS mitigation requests among all available DOTS servers is suboptimal.

* Sequentially contacting DOTS servers may increase the delay before a mitigation plan is enforced.

2. Identify DOTS deployment schemes in a multi-homing context, where DOTS service can be offered by all or a subset of upstream providers.

3. Sketch guidelines and recommendations for placing DOTS requests in multi-homed networks, e.g.,:

* Select the appropriate DOTS server(s).

* Identify cases where anycast is not recommended.



To that aim, this document adopts the following methodology:

o Identify and extract viable deployment candidates from [I-D.ietf-dots-use-cases].

o Augment the description with multi-homing technicalities, e.g.,

* One vs. multiple upstream network providers

* One vs. multiple interconnect routers

* Provider-Independent (PI) vs. Provider-Aggregatable (PA)

o Describe the recommended behavior of DOTS clients and gateways for each case.

Multi-homed DOTS agents are assumed to make use of the protocols defined in [I-D.ietf-dots-signal-channel] and [I-D.ietf-dots-data-channel]; no specific extension is required to the base DOTS protocols for deploying DOTS in a multihomed context.

2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119][RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Terminology

This document makes use of the terms defined in [I-D.ietf-dots-architecture] and [RFC4116].

IP refers to both IPv4 and IPv6.

4. Multi-Homing Scenarios

This section briefly describes some multi-homing scenarios that are relevant to DOTS. In the following sub-sections, only the connections of border routers are shown; internal network topologies are not elaborated hereafter.





o The home network is connected to the Internet using one single CPE (Customer Premises Equipment).

o The CPE is connected to multiple provisioning domains (i.e. both fixed and mobile networks). Provisioning domain (PvD) is explained in [RFC7556].

o Each of these provisioning domains assign IP addresses/prefixes to the CPE. These addresses/prefixes are said to be Provider- Aggregatable (PA).

o The CPE is provided by each of these provisioning domains with additional configuration information such as a list of DNS servers, DNS suffixes associated with the network, default gateway address, and DOTS server’s name [I-D.boucadair-dots-server-discovery].

o Because of ingress filtering, packets forwarded by the CPE to a given provisioning domain must be send with a source IP address that was assigned by that network [RFC8043].

+-------+ +-------+ |Fixed | |Mobile | |Network| |Network| +---+---+ +---+---+ | | Service Providers ............|....................|....................... +---------++---------+ Home Network || +--++-+ | CPE | +-----+ ... (Internal Network)

Figure 2: Typical Multi-homed Residential CPE



o The enterprise network is connected to the Internet using one single router.

o That router is connected to multiple provisioning domains (i.e. managed by distinct administrative entities).



Unlike the previous scenario, two sub-cases can be considered for an enterprise network with regards to assigned addresses:

1. Provider Independent (PI) addresses: The enterprise is the owner of the IP addresses/prefixes; the same address/prefix is then used for communication placed using any of the provisioning domains.

2. PA addresses/prefixes: each of provisioning domains assigns IP addresses/prefixes to the enterprise network.

+------+ +------+ | ISP1 | | ISP2 | +---+--+ +--+---+ | | Service Providers ............|....................|....................... +---------++---------+ Enterprise Network || +--++-+ | rtr | +-----+ ... (Internal Network)

Figure 3: Multi-homed Enterprise Network (Single CPE connected to Multiple Networks)


This scenario is similar to the one in Section 4.2; the main difference is that dedicated routers are used to connect to each provisioning domain.

+------+ +------+ | ISP1 | | ISP2 | +---+--+ +--+---+ | | Service Providers ......................|..........|....................... | | Enterprise Network +---+--+ +--+---+ | rtr1 | | rtr2 | +------+ +------+

... (Internal Network)

Figure 4: Multi-homed Enterprise Network (Multiple CPEs, Multiple ISPs)



4.4. Multi-homed Enterprise with the Same ISP

This scenario is a variant of Section 4.2 and Section 4.3 in which multi-homing is provided by the same ISP (i.e., same provisioning domain).

5. DOTS Deployment Considerations

Table 1 provides some sample (non-exhaustive) deployment schemes to illustrate how DOTS agents may be deployed for each of the scenarios introduced in Section 4.

+---------------------------+-------------------------+-------------+ | Scenario | DOTS client | DOTS | | | | gateway | +---------------------------+-------------------------+-------------+ | Residential CPE | CPE | N/A | +---------------------------+-------------------------+-------------+ | Single CPE, Multiple | internal hosts or CPE | CPE | | provisioning domains | | | +---------------------------+-------------------------+-------------+ | Multiple CPEs, Multiple | internal hosts or all | CPEs (rtr1 | | provisioning domains | CPEs (rtr1 and rtr2) | and rtr2) | +---------------------------+-------------------------+-------------+ | Multi-homed enterprise, | internal hosts or all | CPEs (rtr1 | | Single provisioning | CPEs (rtr1 and rtr2) | and rtr2) | | domain | | | +---------------------------+-------------------------+-------------+

Table 1: Sample Deployment Cases

These deployment schemes are further discussed in the following sub- sections.


Figure 5 depicts DOTS signaling sessions that are required to be established between a DOTS client (C) and DOTS servers (S1, S2) in the context of the scenario described in Section 4.1.

The DOTS client MUST resolve the DOTS server’s name provided by a provisioning domain ([I-D.boucadair-dots-server-discovery]) using the DNS servers learned from the same provisioning domain. The DOTS client MUST use the source address selection algorithm defined in [RFC6724] to select the candidate source addresses to contact each of these DOTS servers. DOTS signaling sessions must be established and maintained with each of the DOTS servers because the mitigation scope of these servers is restricted. The DOTS client SHOULD use the



certificate provisioned by a provisioning domain to authenticate itself to the DOTS server provided by the same provisioning domain. When conveying a mitigation request to protect the attack target(s), the DOTS client among the DOTS servers available MUST select a DOTS server whose network has assigned the prefixes from which target prefixes and target IP addresses are derived. For example, mitigation request to protect target resources bound to a PA IP address/prefix cannot be honored by an provisioning domain other than the one that owns those addresses/prefixes. Consequently, Typically, if a CPE detects a DDoS attack on all its network attachments, it must contact both DOTS servers for mitigation. Nevertheless, if the DDoS attack is received from one single network, then only the DOTS server of that network must be contacted.

The DOTS client MUST be able to associate a DOTS server with each provisioning domain. For example, if the DOTS client is provisioned with S1 using DHCP when attaching to a first network and with S2 using Protocol Configuration Option (PCO) when attaching to a second network, the DOTS client must record the interface from which a DOTS server was provisioned. DOTS signaling session to a given DOTS server must be established using the interface from which the DOTS server was provisioned.

+--+ -----------|S1| / +--+ / / +---+/ | C | +---+\ \ \ \ +--+ -----------|S2| +--+

Figure 5: DOTS associations for a multihomed residential CPE


Figure 6 illustrates a first set of DOTS associations that can be established with a DOTS gateway is enabled in the context of the scenario described in Section 4.2. This deployment is characterized as follows:

o One of more DOTS clients are enabled in hosts located in the internal network.



o A DOTS getaway is enabled to aggregate/relay the requests to upstream DOTS servers.

When PA addresses/prefixes are in used, the same considerations discussed in Section 5.1 are to be followed by the DOTS gateway to contact its DOTS server(s). The DOTS gateways can be reachable from DOTS client using a unicast or anycast address.

Nevertheless, when PI addresses/prefixes are assigned, the DOTS gateway MUST sent the same request to all its DOTS servers.

+--+ -----------|S1| +---+ / +--+ | C1|----+ / +---+ | / +---+ +-+-+/ | C3|------| G | +---+ +-+-+\ +---+ | \ | C2|----+ \ +---+ \ +--+ -----------|S2| +--+

Figure 6: Multiple DOTS Clients, Single DOTS Gateway, Multiple DOTS Servers

An alternate deployment model is depicted in Figure 7. This deployment assumes that:

o One of more DOTS clients are enabled in hosts located in the internal network. These DOTS client may use [I-D.boucadair-dots-server-discovery] to discover its DOTS server(s).

o These DOTS clients communicate directly with upstream DOTS servers.

If PI addresses/prefixes are in use, the DOTS client can send the mitigation request for all its PI addresses/prefixes to any one of the DOTS servers. The use of anycast addresses is NOT RECOMMENDED.

If PA addresses/prefxies are used, the same considerations discussed in Section 5.1 are to be followed by the DOTS clients. Because DOTS clients are not located on the CPE and multiple addreses/prefixes may not be assigned to the DOTS client (IPv4 context, typically), some complications arise to steer the traffic to the appropriate DOTS



server using the appropriate source IP address. These complications discussed in [RFC4116] are not specific to DOTS .

+--+ +--------|C1|--------+ | +--+ | +--+ +--+ +--+ |S2|------|C3|------|S1| +--+ +--+ +--+ | +--+ | +--------|C2|--------+ +--+

Figure 7: Multiple DOTS Clients, Multiple DOTS Servers

Another deployment approach is to enable many DOTS clients; each of them responsible to handle communication with a specific DOTS server (see Figure 8). Each DOTS client is provided with policies (e.g., prefix filter) that will trigger DOTS communications with the DOTS servers. The CPE MUST select the appropriate source IP address when forwarding DOTS messages received from an internal DOTS client. If anycast addresses are used to reach DOTS servers, the CPE may not be able to select the appropriate provisioning domain to which the mitigation request should be forwarded. As a consequence, the request may not be forwarded to the appropriate DOTS server.

+--+ +--------|C1| | +--+ +--+ +--+ +--+ |S2| |C2|------|S1| +--+ +--+ +--+

Figure 8: Single Homed DOTS Clients


The deployments depicted in Figure 7 and Figure 8 apply also for the scenario described in Section 4.3. One specific problem for this scenario is to select the appropriate exit router when contacting a given DOTS server.

An alternative deployment scheme is shown in Figure 9:

o DOTS clients are enabled in hosts located in the internal network.

o A DOTS gateway is enabled in each CPE (rtr1, rtr2).



o Each of these DOTS gateways communicate with the DOTS server of the provisioning domain.

When PI addresses/prefixes are used, DOTS clients can contact any of the DOTS gateways to send a DOTS message. DOTS gateway will then relay the request to the DOTS server. Note that the use of anycast addresses is NOT RECOMMENDED to establish DOTS signaling sessions between DOTS client and DOTS gateways.

When PA addresses/prefixes are used, but no filter rules are provided to DOTS clients, these later MUST contact all DOTS gateways simultaneously to send a DOTS message. Upon receipt of a request by a DOTS gateway, it MUST check whether the request is to be forwarded upstream or be rejected.

When PA addresses/prefixes are used, but specific filter rules are provided to DOTS clients using some means that are out of scope, these later MUST select the appropriate DOTS gateway to be contacted. The use of anycast is NOT RECOMMENDED to reach DOTS gateways.

+---+ +------------| C1|----+ | +---+ | +--+ +-+-+ +---+ +-+-+ +--+ |S2|------|G2 |------| C3|------|G1 |------|S1| +--+ +-+-+ +---+ +-+-+ +--+ | +---+ | +------------| C2|----+ +---+

Figure 9: Multiple DOTS Clients, Multiple DOTS Gateways, Multiple DOTS Servers

5.4. Multi-homed Enterprise: Single ISP

The key difference of the scenario described in Section 4.4 compared to the other scenarios is that multi-homing is provided by the same ISP. Concretely, that ISP can decided to provision the enterprise network with:

1. The same DOTS server for all network attachments.

2. Distinct DOTS servers for each network attachment. These DOTS servers needs to coordinate when a mitigation action is received from the enterprise network.



In both cases, DOTS agents enabled within the enterprise network may decide to select one or all network attachments to place DOTS mitigation requests.


DOTS-related security considerations are discussed in Section 4 of [I-D.ietf-dots-architecture].

TBD: In Home networks, if EST is used then how will the DOTS gateway (EST client) be provisioned with credentials for initial enrolment (see Section 2.2 in RFC 7030).


This document does not require any action from IANA.

8. Acknowledgements

Thanks to Roland Dobbins and Nik Teague for sharing their comments on the mailing list.

Thanks to Kirill Kasavchenko for the comments.

9. References


[I-D.ietf-dots-architecture] Mortensen, A., Andreasen, F., K, R., [email protected], c., Compton, R., and N. Teague, "Distributed-Denial-of-Service Open Threat Signaling (DOTS) Architecture", draft-ietf-dots- architecture-07 (work in progress), September 2018.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>.

[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown, "Default Address Selection for Internet Protocol Version 6 (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012, <https://www.rfc-editor.org/info/rfc6724>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>.




[I-D.boucadair-dots-server-discovery] Boucadair, M., K, R., and P. Patil, "Distributed-Denial- of-Service Open Threat Signaling (DOTS) Server Discovery", draft-boucadair-dots-server-discovery-04 (work in progress), April 2018.

[I-D.ietf-dots-data-channel] Boucadair, M., K, R., Nishizuka, K., Xia, L., Patil, P., Mortensen, A., and N. Teague, "Distributed Denial-of- Service Open Threat Signaling (DOTS) Data Channel Specification", draft-ietf-dots-data-channel-22 (work in progress), September 2018.

[I-D.ietf-dots-signal-channel] K, R., Boucadair, M., Patil, P., Mortensen, A., and N. Teague, "Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification", draft- ietf-dots-signal-channel-25 (work in progress), September 2018.

[I-D.ietf-dots-use-cases] Dobbins, R., Migault, D., Fouant, S., Moskowitz, R., Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS Open Threat Signaling", draft-ietf-dots-use-cases-16 (work in progress), July 2018.

[RFC3582] Abley, J., Black, B., and V. Gill, "Goals for IPv6 Site- Multihoming Architectures", RFC 3582, DOI 10.17487/RFC3582, August 2003, <https://www.rfc-editor.org/info/rfc3582>.

[RFC4116] Abley, J., Lindqvist, K., Davies, E., Black, B., and V. Gill, "IPv4 Multihoming Practices and Limitations", RFC 4116, DOI 10.17487/RFC4116, July 2005, <https://www.rfc-editor.org/info/rfc4116>.

[RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet Denial-of-Service Considerations", RFC 4732, DOI 10.17487/RFC4732, December 2006, <https://www.rfc-editor.org/info/rfc4732>.

[RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015, <https://www.rfc-editor.org/info/rfc7556>.



[RFC8043] Sarikaya, B. and M. Boucadair, "Source-Address-Dependent Routing and Source Address Selection for IPv6 Hosts: Overview of the Problem Space", RFC 8043, DOI 10.17487/RFC8043, January 2017, <https://www.rfc-editor.org/info/rfc8043>.







Network Working Group M. BoucadairInternet-Draft OrangeIntended status: Standards Track T. ReddyExpires: January 17, 2018 McAfee P. Patil Cisco July 16, 2017

Distributed-Denial-of-Service Open Threat Signaling (DOTS) Server Discovery draft-boucadair-dots-server-discovery-02

Abstract

It may not be possible for a network to determine the cause for an attack, but instead just realize that some resources seem to be under attack. To fill that gap, Distributed-Denial-of-Service Open Threat Signaling (DOTS) allows a network to inform a DOTS server that it is under a potential attack so that appropriate mitigation actions are undertaken.

This document specifies mechanisms to configure nodes with DOTS servers.

Status of This Memo





Copyright Notice


Boucadair, et al. Expires January 17, 2018 [Page 1]

Internet-Draft DOTS Server Discovery July 2017

This document is subject to BCP 78 and the IETF Trust’s Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Why Multiple Discovery Mechanisms? . . . . . . . . . . . . . 4 5. Discovery Procedure . . . . . . . . . . . . . . . . . . . . . 7 6. Resolution . . . . . . . . . . . . . . . . . . . . . . . . . 8 7. Discovery using Service Resolution . . . . . . . . . . . . . 10 7.1. Retrieving Domain Name . . . . . . . . . . . . . . . . . 10 7.1.1. DHCP . . . . . . . . . . . . . . . . . . . . . . . . 10 8. DNS Service Discovery . . . . . . . . . . . . . . . . . . . . 11 8.1. DNS-SD . . . . . . . . . . . . . . . . . . . . . . . . . 11 8.2. mDNS . . . . . . . . . . . . . . . . . . . . . . . . . . 11 9. DHCP Options for DOTS . . . . . . . . . . . . . . . . . . . . 11 9.1. DHCPv6 DOTS Option . . . . . . . . . . . . . . . . . . . 12 9.1.1. Format . . . . . . . . . . . . . . . . . . . . . . . 12 9.1.2. DHCPv6 Client Behavior . . . . . . . . . . . . . . . 12 9.2. DHCPv4 DOTS Option . . . . . . . . . . . . . . . . . . . 13 9.2.1. Format . . . . . . . . . . . . . . . . . . . . . . . 13 9.2.2. DHCPv4 Client Behavior . . . . . . . . . . . . . . . 13 10. Anycast . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 11. Security Considerations . . . . . . . . . . . . . . . . . . . 14 11.1. DHCP . . . . . . . . . . . . . . . . . . . . . . . . . . 15 11.2. Service Resolution . . . . . . . . . . . . . . . . . . . 15 11.3. DNS Service Discovery . . . . . . . . . . . . . . . . . 15 11.4. Anycast . . . . . . . . . . . . . . . . . . . . . . . . 15 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 12.1. DHCPv6 Option . . . . . . . . . . . . . . . . . . . . . 16 12.2. DHCPv4 Option . . . . . . . . . . . . . . . . . . . . . 16 12.3. Application Service & Application Protocol Tags . . . . 16 12.3.1. DOTS Application Service Tag Registration . . . . . 16 12.3.2. signal.udp Application Protocol Tag Registration . . 16 12.3.3. signal.tcp Application Protocol Tag Registration . . 17 12.3.4. data.tcp Application Protocol Tag Registration . . . 17 12.4. IPv4 Anycast . . . . . . . . . . . . . . . . . . . . . . 17 12.5. IPv6 Anycast . . . . . . . . . . . . . . . . . . . . . . 18 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18



14. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 14.1. Normative References . . . . . . . . . . . . . . . . . . 18 14.2. Informative References . . . . . . . . . . . . . . . . . 19 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 21

1. Introduction

In many deployments, it may not be possible for a network to determine the cause for a distributed Denial-of-Service (DoS) attack [RFC4732], but instead just realize that some resources seem to be under attack. To fill that gap, the IETF is specifying an architecture, called DDoS Open Threat Signaling (DOTS) [I-D.ietf-dots-architecture], in which a DOTS client can inform a DOTS server that the network is under a potential attack and that appropriate mitigation actions are required. Indeed, because the lack of a common method to coordinate a real-time response among involved actors and network domains inhibits the effectiveness of DDoS attack mitigation, DOTS protocol is meant to carry requests for DDoS attack mitigation, thereby reducing the impact of an attack and leading to more efficient defensive actions. [I-D.ietf-dots-use-cases] identifies a set of scenarios for DOTS.




[I-D.ietf-dots-architecture] specifies that the DOTS client may be provided with a list of DOTS servers; each associated with one or more IP addresses. These addresses may or may not be of the same address family. The DOTS client establishes one or more DOTS sessions by connecting to the provided DOTS server addresses. The logic for connecting to one or multiple IP addresses is out of scope of this document.

This document specifies methods for DOTS clients to discover their DOTS server(s). The rationale for specifying multiple discovery mechanisms is discussed in Section 4.



Considerations for the selection of DOTS server(s) by multi-homed DOTS client is out of scope; the reader should refer to [I-D.boucadair-dots-multihoming] for more details.


The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

3. Terminology

This document makes use of the following terms:

o DDoS: A distributed Denial-of-Service attack, in which traffic originating from multiple sources are directed at a target on a network. DDoS attacks are intended to cause a negative impact on the availability of servers, services, applications, and/or other functionality of an attack target. o DHCP refers to both DHCPv4 [RFC2131] and DHCPv6 [RFC3315]. o DHCP client denotes a node that initiates requests to obtain configuration parameters from one or more DHCP servers. o DHCP server refers to a node that responds to requests from DHCP clients. o DOTS client: A DOTS-aware software module responsible for requesting attack response coordination with other DOTS-aware elements. o DOTS server: A DOTS-aware software module handling and responding to messages from DOTS clients. The DOTS server should enable mitigation on behalf of the DOTS client, if requested, by communicating the DOTS client’s request to the mitigator and returning selected mitigator feedback to the requesting DOTS client. A DOTS server may also be a mitigator. o DOTS gateway: A DOTS-aware software module that is logically equivalent to a DOTS client back-to-back with a DOTS server.

The reader should be familiar with other terms defined in [I-D.ietf-dots-architecture] and [RFC3958].

4. Why Multiple Discovery Mechanisms?

It is tempting to specify one single discovery mechanism for DOTS. Nevertheless, the analysis of the various use cases sketched in [I-D.ietf-dots-use-cases] reveals that it is unlikely that one single discovery method can be suitable for all the sample deployments (Table 1). Concretely:



o Some of the use cases may allow DOTS clients to have direct communications with upstream DOTS servers; that is no DOTS gateway is involved. Leveraging on existing features that do not require specific feature on the node embedding the DOTS client may ease DOTS deployment. Typically, the use of Straightforward-Naming Authority Pointer (S-NAPTR) lookups [RFC3958] allows the DOTS server administrators provision the preferred DOTS signal channel transport protocol between the DOTS client and the DOTS server and allows the DOTS client to discover this preference.

o Resolving a DOTS server domain name offered by the upstream transit provider provisioned to a DOTS client into IP address(es) require the use of the appropriate DNS resolvers; otherwise, resolving those names will fail. The use of protocols such as DHCP does allow to associate provisioned DOTS server domain names with a list of DNS servers to be used for name resolution.

o The upstream network provider is not the DDoS mitigation provider for some of these use cases. The use of anycast is not appropriate for this use case, in particular. It is safe to assume that for such deployments, the DOTS server(s) domain name is provided during the service subscription (i.e., manual/local configuration).

o Multiple DOTS clients may be enabled within a network (e.g., enterprise network). Automatic means to discover DOTS servers in a deterministic manner are interesting from an operational standpoint.

o Some of the use cases may involve a DOTS gateway that is responsible for forking requests received from DOTS clients to upstream DOTS servers or for selecting the appropriate DOTS server. Particularly, the use of anycast may simplify the operations within the enterprise network to discover a DOTS gateway, if the enterprise network is single-homed.

o Many use cases discussed in [I-D.ietf-dots-use-cases] do involve a CPE device. Multiple CPEs, connected to distinct network providers may even be considered. It is intuitive to leverage on existing mechanisms such as discovery using service resolution or DHCP or anycast to provision the CPE acting as a DOTS client with the DOTS server(s).



o DNS Service Discovery.

o Discovery using DHCP Options.

o A mechanism based on anycast address for DOTS usage.

5. Discovery Procedure

In order to encourage consistent DOTS behaviors while allowing for automated DOTS server discovery, the following procedure MUST be followed by a DOTS client to build a DOTS server(s) list to contact:

1. Explicit configuration:

* Local/Manual Configuration: A DOTS client, by default, will learn the DOTS server(s) by means of local or manual DOTS configuration (i.e., DOTS servers configured at the system level). Configuration discovered from a DOTS client application is considered as local configuration. An implementation may give the user an opportunity (e.g., by means of configuration file options or menu items) to specify DOTS server(s) for each address family.

* DHCP: The DOTS client attempts to discover DOTS server(s) names from DHCP by including a DOTS option code in the Option Request for IPv6 and Parameter Request List Option for IPv4, respectively.

2. Service Resolution : The DOTS client attempts to perform DOTS service resolution using the client’s DNS domain or DOTS server name. The DOTS server name can be discovered either using local/ manual configuration or DHCP DOTS options.

3. DNS SD: DNS Service Discovery.

4. Anycast : Send DOTS request to establish a DOTS session with the assigned DOTS server anycast address for each combination of interface and address family.

The above procedure MUST also be followed by a DOTS gateway.

The document does not prescribe a strict order that a client must follow for discovery. An implementation may choose to perform all the above steps in parallel for discovery OR choose to follow any desired order and stop the discovery procedure if a mechanism succeeds.



On hosts with more than one interface or address family (IPv4/v6), the DOTS server discovery procedure has to be performed for each combination of interface and address family. A client MAY choose to perform the discovery procedure only for a desired interface/address combination if the client does not wish to discover a DOTS server for all combinations of interface and address family.

6. Resolution

Once the DOTS client has retrieved client’s DNS domain or discovered the DOTS server name using local/manual configuration or DHCP DOTS options, an S-NAPTR lookup with ’DOTS’ application service and the desired protocol tag is made to obtain information necessary to connect to the authoritative DOTS server within the given domain.

This specification defines "DOTS" as an application service tag (Section 12.3.1) and "signal.udp" (Section 12.3.2), "signal.tcp" (Section 12.3.3), and "data.tcp" (Section 12.3.4) as application protocol tags.



In the example below, for domain ’example.net’, the resolution algorithm will result in IP address(es), port, tag and protocol tuples as follows:

example.net. IN NAPTR 100 10 "" DOTS:signal.udp "" signal.example.net. IN NAPTR 200 10 "" DOTS:signal.tcp "" signal.example.net. IN NAPTR 300 10 "" DOTS:data.tcp "" data.example.net.

signal.example.net. IN NAPTR 100 10 S DOTS:signal.udp "" _dots._signal._udp.example.net. IN NAPTR 200 10 S DOTS:signal.tcp "" _dots._signal._tcp.example.net.

data.example.net. IN NAPTR 100 10 S DOTS:data.tcp "" _dots._data._tcp.example.net.

_dots._signal._udp.example.net. IN SRV 0 0 5000 a.example.net.

_dots._signal._tcp.example.net. IN SRV 0 0 5001 a.example.net.

_dots._data._tcp.example.net. IN SRV 0 0 5002 a.example.net.

a.example.net. IN AAAA 2001:db8::1

+-------+----------+-------------+------+--------+ | Order | Protocol | IP address | Port | Tag | +-------+----------+-------------+------+--------+ | 1 | UDP | 2001:db8::1 | 5000 | Signal | | 2 | TCP | 2001:db8::1 | 5001 | Signal | | 3 | TCP | 2001:db8::1 | 5002 | Data | +-------+----------+-------------+------+--------+

If no DOTS-specific S-NAPTR records can be retrieved, the discovery procedure fails for this domain name (and the corresponding interface and IP protocol version). If more domain names are known, the discovery procedure MAY perform the corresponding S-NAPTR lookups immediately. However, before retrying a lookup that has failed, a DOTS client MUST wait a time period that is appropriate for the encountered error (e.g., NXDOMAIN, timeout, etc.).



7. Discovery using Service Resolution

This mechanism is performed in two steps:

1. A DNS domain name is retrieved for each combination of interface and address family.

2. Retrieved DNS domain names are then used for S-NAPTR lookups. Further DNS lookups may be necessary to determine DOTS server IP address(es).

7.1. Retrieving Domain Name

A DOTS client has to determine the domain in which it is located. The following section describes the means to obtain the domain name from DHCP. Other means of retrieving domain names may be used, which are outside the scope of this document, e.g., local configuration.

Implementations MAY allow the user to specify a default name that is used, if no specific name has been configured.

7.1.1. DHCP

DHCP can be used to determine the domain name related to an interface’s point of network attachment. Network operators may provide the domain name to be used for service discovery within an access network using DHCP. Sections 3.2 and 3.3 of [RFC5986] define DHCP IPv4 and IPv6 access network domain name options, OPTION_V4_ACCESS_DOMAIN and OPTION_V6_ACCESS_DOMAIN respectively, to identify a domain name that is suitable for service discovery within the access network.

For IPv4, the discovery procedure MUST request the access network domain name option in a Parameter Request List option, as described in [RFC2131]. [RFC2132] defines the DHCP IPv4 domain name option; while this option is less suitable, a client MAY request for it if the access network domain name defined in [RFC5986] is not available.

For IPv6, the discovery procedure MUST request for the access network domain name option in an Options Request Option (ORO) within an Information-request message, as described in [RFC3315].

If neither option can be retrieved the procedure fails for this interface. If a result can be retrieved it will be used as an input for S-NAPTR resolution discussed in Section 6.



8. DNS Service Discovery

DNS-based Service Discovery (DNS-SD) [RFC6763] and Multicast DNS (mDNS) [RFC6762] provide generic solutions for discovering services. DNS-SD/mDNS define a set of naming rules for certain DNS record types that they use for advertising and discovering services.

8.1. DNS-SD

Section 4.1 of [RFC6763] specifies that a service instance name in DNS-SD has the following structure:

<Instance> . <Service> . <Domain>

The <Domain> portion specifies the DNS sub-domain where the service instance is registered. It may be "local.", indicating the mDNS local domain, or it may be a conventional domain name such as "example.com.".

The <Service> portion of the DOTS service instance name MUST be "_dots._signal._udp" or "_dots._signal._tcp" or "_dots._data._tcp".

8.2. mDNS

A DOTS client can proactively discover DOTS servers being advertised in the site by multicasting a PTR query to one or all of the following:

o "_dots._signal._udp.local."

o "_dots._signal._tcp.local."

o "_dots._data._tcp.local."

A DOTS server can send out gratuitous multicast DNS answer packets whenever it starts up, wakes from sleep, or detects a change in network configuration. DOTS clients receive these gratuitous packets and cache information contained in it.

9. DHCP Options for DOTS

The DOTS server name retrieved using DHCPv6 or DHCPv4 DOTS options will be used as an input for S-NAPTR resolution discussed in Section 6.



9.1. DHCPv6 DOTS Option

9.1.1. Format

The DHCPv6 DOTS option is used to configure a name of the DOTS server. The format of this option is shown in Figure 2.

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_V6_DOTS | Option-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | dots-server-name (FQDN) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: DHCPv6 DOTS option

The fields of the option shown in Figure 2 are as follows:

o Option-code: OPTION_V6_DOTS (TBA, see Section 12.1) o Option-length: Length of the dots-server-name field in octets. o dots-server-name: A fully qualified domain name of the DOTS server. This field is formatted as specified in Section 8 of [RFC3315].

An example of the dots-server-name encoding is shown in Figure 3. This example conveys the FQDN "dots.example.com.".

+------+------+------+------+------+------+------+------+------+ | 0x04 | d | o | t | s | 0x07 | e | x | a | +------+------+------+------+------+------+------+------+------+ | m | p | l | e | 0x03 | c | o | m | 0x00 | +------+------+------+------+------+------+------+------+------+

Figure 3: An example of the dots-server-name encoding

9.1.2. DHCPv6 Client Behavior

DHCP clients MAY request option OPTION_V6_DOTS, as defined in [RFC3315], Sections 17.1.1, 18.1.1, 18.1.3, 18.1.4, 18.1.5, and 22.7. As a convenience to the reader, it is mentioned here that the DHCP client includes the requested option codes in the Option Request Option.

If the DHCP client receives more than one OPTION_V6_DOTS option, it MUST use only the first instance of that option.



If the OPTION_V6_DOTS option contains more than one name, as distinguished by the presence of multiple root labels, the DHCP client MUST use only the first name. Once the name is validated (Section 8 of [RFC3315]), the name is passed to a name resolution library.

9.2. DHCPv4 DOTS Option

9.2.1. Format

The DHCPv4 DOTS option is used to configure a name of the DOTS server. The format of this option is illustrated in Figure 4.

Code Length DOTS server name +-----+-----+-----+-----+-----+-----+-----+-- | TBA | n | s1 | s2 | s3 | s4 | s5 | ... +-----+-----+-----+-----+-----+-----+-----+--

The values s1, s2, s3, etc. represent the domain name labels in the domain name encoding.

Figure 4: DHCPv4 DOTS option


o Code: OPTION_V4_DOTS (TBA, see Section 12.2); o Length: Includes the length of the "DOTS server name" field in octets; the maximum length is 255 octets. o DOTS server name: The domain name of the DOTS server. This field is formatted as specified in Section 8 of [RFC3315].


To discover a DOTS server, the DHCPv4 client MUST include OPTION_V4_DOTS in a Parameter Request List Option [RFC2132].

If the DHCP client receives more than one OPTION_V4_DOTS option, it MUST use only the first instance of that option.

If the OPTION_V4_DOTS option contains more than one name, as distinguished by the presence of multiple root labels, the DHCP client MUST use only the first FQDN. Once the name is validated (Section 8 of [RFC3315]), the name is passed to a name resolution library.



10. Anycast

IP anycast can also be used for DOTS service discovery. A packet sent to an anycast address is delivered to the ’topologically nearest’ network interface with the anycast address.

When a DOTS client requires DOTS services, it attempts to establish a signaling session with the assigned anycast address(es) defined in Sections 12.4 and 12.5. A DOTS server, that receives a DOTS request with an anycast address, SHOULD redirect the DOTS client to the appropriate DOTS unicast server(s) using the mechanism described in Section 5.5 of [I-D.ietf-dots-signal-channel], unless it is configured otherwise. Indeed, a DOTS server SHOULD be configurable to maintain all DOTS communications using anycast. DOTS redirect is not made mandatory because the use of anycast is not problematic for some deployment scenarios such as an enterprise network deploying one single DOTS gateway connected to one single network provider.

[I-D.boucadair-dots-multihoming] identifies a set of deployment schemes in which the use of anycast is not recommended.


DOTS-related security considerations are discussed in Section 4 of [I-D.ietf-dots-architecture] is to be considered. DOTS agents must authenticate each other using (D)TLS before a DOTS session is considered valid.

If the DOTS client is explicitly configured with DOTS server(s) then the DOTS client can also be explicitly configured with credentials to authenticate the DOTS server.

The CPE device acting as a DOTS client MAY use Bootstrapping Remote Secure Key Infrastructures (BRSKI) discussed in [I-D.ietf-anima-bootstrapping-keyinfra] to automatically bootstrap using the vendor installed X.509 certificate, in combination with a domain registrar provided by the upstream transit provider and vendor’s authorizing service. The CPE device authenticates to the upstream transit provider using the vendor installed X.509 certificate and the upstream transit provider validates the vendor installed certificate on the CPE device using the Manufacturer Authorized Signing Authority (MASA) service. If authentication is successful then the CPE device can request and get a voucher from the MASA service via the domain registrar. The voucher is signed by the MASA service and includes the upstream transit provider’s trust anchor certificate. The CPE device validates the signed voucher using the manufacturer installed trust anchor associated with the vendor’s selected MASA service and stores the upstream transit



provider’s trust anchor certificate. The CPE device then uses Enrollment over Secure Transport (EST) [RFC7030] for certificate enrollment (Section 3.8 in [I-D.ietf-anima-bootstrapping-keyinfra]). The DOTS client on the CPE device can authenticate to the DOTS server using the certificate provisioned by the EST server and the DOTS client can validate the DOTS server certificate using the upstream transit provider’s trust anchor certificate it had received in the voucher.

11.1. DHCP

The security considerations in [RFC2131] and [RFC3315] are to be considered.

11.2. Service Resolution

The primary attack against the methods described in Section 7 is one that would lead to impersonation of a DOTS server. An attacker could attempt to compromise the S-NAPTR resolution. The use of mutual authentication makes it difficult to redirect a DOTS client to an illegitimate DOTS server.

11.3. DNS Service Discovery

Since DNS-SD is just a specification for how to name and use records in the existing DNS system, it has no specific additional security requirements over and above those that already apply to DNS queries and DNS updates. For DNS queries, DNS Security Extensions (DNSSEC) [RFC4033] SHOULD be used where the authenticity of information is important. For DNS updates, secure updates [RFC2136][RFC3007] SHOULD generally be used to control which clients have permission to update DNS records.

For mDNS, in addition to what has been described above, a principal security threat is a security threat inherent to IP multicast routing and any application that runs on it. A rogue system can advertise that it is a DOTS server. Discovery of such rogue systems as DOTS servers, in itself, is not a security threat if the DOTS client authenticates the discovered DOTS servers.

11.4. Anycast

Anycast-related security considerations are discussed in [RFC4786] and [RFC7094].




IANA is requested to allocate the SRV service name of "_dots._signal" for DOTS signal channel over UDP or TCP, and the service name of "_dots._data" for DOTS data channel over TCP.

12.1. DHCPv6 Option

IANA is requested to assign the following new DHCPv6 Option Code in the registry maintained in http://www.iana.org/assignments/ dhcpv6-parameters:

Option Name Value -------------- ----- OPTION_V6_DOTS TBA

12.2. DHCPv4 Option

IANA is requested to assign the following new DHCPv4 Option Code in the registry maintained in http://www.iana.org/assignments/bootp- dhcp-parameters/:

Option Name Value Data length Meaning -------------- ----- ------------------------- ---------------------- OPTION_V4_DOTS TBA Variable; the maximum Includes the name of length is 255 octets. the DOTS server.

12.3. Application Service & Application Protocol Tags

This document requests IANA to make the following allocations from the registry available at: https://www.iana.org/assignments/s-naptr- parameters/s-naptr-parameters.xhtml.

12.3.1. DOTS Application Service Tag Registration

o Application Protocol Tag: DOTS

o Intended Usage: See Section 6

o Security Considerations: See Section 11

o Contact Information: <one of the authors>

12.3.2. signal.udp Application Protocol Tag Registration

o Application Protocol Tag: signal.udp




12.5. IPv6 Anycast

IANA has assigned a single IPv6 address from the 2001:0000::/23 prefix and registered it in the "IANA IPv6 Special-Purpose Address Registry" [RFC6890].


13. Acknowledgements

Thanks to Brian Carpenter for the review of the BRSKI text.

14. References


[I-D.ietf-dots-architecture] Mortensen, A., Andreasen, F., Reddy, T., [email protected], c., Compton, R., and N. Teague, "Distributed-Denial-of-Service Open Threat Signaling (DOTS) Architecture", draft-ietf-dots- architecture-04 (work in progress), July 2017.


[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, DOI 10.17487/RFC2131, March 1997, <http://www.rfc-editor.org/info/rfc2131>.



[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997, <http://www.rfc-editor.org/info/rfc2132>.

[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 2003, <http://www.rfc-editor.org/info/rfc3315>.

[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application Service Location Using SRV RRs and the Dynamic Delegation Discovery Service (DDDS)", RFC 3958, DOI 10.17487/RFC3958, January 2005, <http://www.rfc-editor.org/info/rfc3958>.

[RFC5986] Thomson, M. and J. Winterbottom, "Discovering the Local Location Information Server (LIS)", RFC 5986, DOI 10.17487/RFC5986, September 2010, <http://www.rfc-editor.org/info/rfc5986>.

[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, DOI 10.17487/RFC6762, February 2013, <http://www.rfc-editor.org/info/rfc6762>.

[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, <http://www.rfc-editor.org/info/rfc6763>.

[RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, "Special-Purpose IP Address Registries", BCP 153, RFC 6890, DOI 10.17487/RFC6890, April 2013, <http://www.rfc-editor.org/info/rfc6890>.


[I-D.boucadair-dots-multihoming] Boucadair, M. and T. Reddy, "Multi-homing Considerations for Distributed-Denial-of-Service Open Threat Signaling (DOTS)", draft-boucadair-dots-multihoming-01 (work in progress), June 2017.

[I-D.ietf-anima-bootstrapping-keyinfra] Pritikin, M., Richardson, M., Behringer, M., Bjarnason, S., and K. Watsen, "Bootstrapping Remote Secure Key Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping- keyinfra-07 (work in progress), July 2017.



[I-D.ietf-dots-data-channel] Reddy, T., Boucadair, M., Nishizuka, K., Xia, L., Patil, P., Mortensen, A., and N. Teague, "Distributed Denial-of- Service Open Threat Signaling (DOTS) Data Channel", draft- ietf-dots-data-channel-02 (work in progress), June 2017.

[I-D.ietf-dots-signal-channel] Reddy, T., Boucadair, M., Patil, P., Mortensen, A., and N. Teague, "Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel", draft-ietf-dots-signal- channel-02 (work in progress), June 2017.


[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, DOI 10.17487/RFC2136, April 1997, <http://www.rfc-editor.org/info/rfc2136>.

[RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic Update", RFC 3007, DOI 10.17487/RFC3007, November 2000, <http://www.rfc-editor.org/info/rfc3007>.

[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, DOI 10.17487/RFC4033, March 2005, <http://www.rfc-editor.org/info/rfc4033>.


[RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786, December 2006, <http://www.rfc-editor.org/info/rfc4786>.

[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March 2011, <http://www.rfc-editor.org/info/rfc6125>.



[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed., "Enrollment over Secure Transport", RFC 7030, DOI 10.17487/RFC7030, October 2013, <http://www.rfc-editor.org/info/rfc7030>.

[RFC7094] McPherson, D., Oran, D., Thaler, D., and E. Osterweil, "Architectural Considerations of IP Anycast", RFC 7094, DOI 10.17487/RFC7094, January 2014, <http://www.rfc-editor.org/info/rfc7094>.

[RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and S. Krishnan, "Guidelines for Creating New DHCPv6 Options", BCP 187, RFC 7227, DOI 10.17487/RFC7227, May 2014, <http://www.rfc-editor.org/info/rfc7227>.






Prashanth Patil Cisco Systems, Inc.



Network Working Group M. BoucadairInternet-Draft OrangeIntended status: Standards Track T. ReddyExpires: April 10, 2019 McAfee P. Patil Cisco October 7, 2018

Distributed-Denial-of-Service Open Threat Signaling (DOTS) Server Discovery draft-boucadair-dots-server-discovery-05

Abstract

It may not be possible for a network to determine the cause for an attack, but instead just realize that some resources seem to be under attack. To fill that gap, Distributed-Denial-of-Service Open Threat Signaling (DOTS) allows a network to inform a DOTS server that it is under a potential attack so that appropriate mitigation actions are undertaken.

This document specifies mechanisms to configure nodes with DOTS servers.

Status of This Memo




This Internet-Draft will expire on April 10, 2019.

Copyright Notice


Boucadair, et al. Expires April 10, 2019 [Page 1]

Internet-Draft DOTS Server Discovery October 2018


Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Why Multiple Discovery Mechanisms? . . . . . . . . . . . . . 5 5. Discovery Procedure . . . . . . . . . . . . . . . . . . . . . 7 6. Resolution . . . . . . . . . . . . . . . . . . . . . . . . . 8 7. Discovery using Service Resolution . . . . . . . . . . . . . 10 7.1. Retrieving Domain Name . . . . . . . . . . . . . . . . . 10 7.1.1. DHCP . . . . . . . . . . . . . . . . . . . . . . . . 10 8. DNS Service Discovery . . . . . . . . . . . . . . . . . . . . 11 8.1. DNS-SD . . . . . . . . . . . . . . . . . . . . . . . . . 11 8.2. mDNS . . . . . . . . . . . . . . . . . . . . . . . . . . 11 9. DHCP Options for DOTS . . . . . . . . . . . . . . . . . . . . 11 9.1. DHCPv6 DOTS Options . . . . . . . . . . . . . . . . . . . 12 9.1.1. Format of DOTS Reference Identifier Option . . . . . 12 9.1.2. Format Format of DOTS Address Option . . . . . . . . 13 9.1.3. DHCPv6 Client Behavior . . . . . . . . . . . . . . . 13 9.2. DHCPv4 DOTS Options . . . . . . . . . . . . . . . . . . . 14 9.2.1. Format of DOTS Reference Identifier Option . . . . . 14 9.2.2. Format Format of DOTS Address Option . . . . . . . . 15 9.2.3. DHCPv4 Client Behavior . . . . . . . . . . . . . . . 16 10. Anycast . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 11. Security Considerations . . . . . . . . . . . . . . . . . . . 17 11.1. DHCP . . . . . . . . . . . . . . . . . . . . . . . . . . 18 11.2. Service Resolution . . . . . . . . . . . . . . . . . . . 18 11.3. DNS Service Discovery . . . . . . . . . . . . . . . . . 18 11.4. Anycast . . . . . . . . . . . . . . . . . . . . . . . . 18 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 12.1. DHCPv6 Option . . . . . . . . . . . . . . . . . . . . . 19 12.2. DHCPv4 Option . . . . . . . . . . . . . . . . . . . . . 19 12.3. Application Service & Application Protocol Tags . . . . 19 12.3.1. DOTS Application Service Tag Registration . . . . . 19 12.3.2. signal.udp Application Protocol Tag Registration . . 20 12.3.3. signal.tcp Application Protocol Tag Registration . . 20 12.3.4. data.tcp Application Protocol Tag Registration . . . 20 12.4. IPv4 Anycast . . . . . . . . . . . . . . . . . . . . . . 20



12.5. IPv6 Anycast . . . . . . . . . . . . . . . . . . . . . . 21 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 14.1. Normative References . . . . . . . . . . . . . . . . . . 22 14.2. Informative References . . . . . . . . . . . . . . . . . 23 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 24

1. Introduction

In many deployments, it may not be possible for a network to determine the cause for a distributed Denial-of-Service (DoS) attack [RFC4732], but instead just realize that some resources seem to be under attack. To fill that gap, the IETF is specifying an architecture, called DDoS Open Threat Signaling (DOTS) [I-D.ietf-dots-architecture], in which a DOTS client can inform a DOTS server that the network is under a potential attack and that appropriate mitigation actions are required. Indeed, because the lack of a common method to coordinate a real-time response among involved actors and network domains inhibits the effectiveness of DDoS attack mitigation, DOTS protocol is meant to carry requests for DDoS attack mitigation, thereby reducing the impact of an attack and leading to more efficient defensive actions. [I-D.ietf-dots-use-cases] identifies a set of scenarios for DOTS.




[I-D.ietf-dots-architecture] specifies that the DOTS client may be provided with a list of DOTS servers; each associated with one or more IP addresses. These addresses may or may not be of the same address family. The DOTS client establishes one or more DOTS sessions by connecting to the provided DOTS server addresses. The logic for connecting to one or multiple IP addresses is out of scope of this document.



This document specifies methods for DOTS clients to discover their DOTS server(s). The rationale for specifying multiple discovery mechanisms is discussed in Section 4.

Considerations for the selection of DOTS server(s) by multi-homed DOTS clients is out of scope; the reader should refer to [I-D.boucadair-dots-multihoming] for more details.

Likewise, happy eyeballs considerations for DOTS are out of scope. The reader should refer to Section 4 of [I-D.ietf-dots-signal-channel].



3. Terminology

This document makes use of the following terms:

o DDoS: A distributed Denial-of-Service attack, in which traffic originating from multiple sources are directed at a target on a network. DDoS attacks are intended to cause a negative impact on the availability of servers, services, applications, and/or other functionality of an attack target. o DHCP refers to both DHCPv4 [RFC2131] and DHCPv6 [RFC3315]. o DHCP client denotes a node that initiates requests to obtain configuration parameters from one or more DHCP servers. o DHCP server refers to a node that responds to requests from DHCP clients. o DOTS client: A DOTS-aware software module responsible for requesting attack response coordination with other DOTS-aware elements. o DOTS server: A DOTS-aware software module handling and responding to messages from DOTS clients. The DOTS server should enable mitigation on behalf of the DOTS client, if requested, by communicating the DOTS client’s request to the mitigator and returning selected mitigator feedback to the requesting DOTS client. A DOTS server may also be a mitigator. o DOTS gateway: A DOTS-aware software module that is logically equivalent to a DOTS client back-to-back with a DOTS server.

Furthermore, the reader should be familiar with other terms defined in [I-D.ietf-dots-architecture] and [RFC3958].



4. Why Multiple Discovery Mechanisms?

It is tempting to specify one single discovery mechanism for DOTS. Nevertheless, the analysis of the various use cases sketched in [I-D.ietf-dots-use-cases] reveals that it is unlikely that one single discovery method can be suitable for all the sample deployments (Table 1). Concretely:

o Some of the use cases may allow DOTS clients to have direct communications with upstream DOTS servers; that is no DOTS gateway is involved. Leveraging on existing features that do not require specific feature on the node embedding the DOTS client may ease DOTS deployment. Typically, the use of Straightforward-Naming Authority Pointer (S-NAPTR) lookups [RFC3958] allows the DOTS server administrators provision the preferred DOTS signal channel transport protocol between the DOTS client and the DOTS server and allows the DOTS client to discover this preference.

o Resolving a DOTS server domain name offered by the upstream transit provider provisioned to a DOTS client into IP address(es) require the use of the appropriate DNS resolvers; otherwise, resolving those names will fail. The use of protocols such as DHCP does allow to associate provisioned DOTS server domain names with a list of DNS servers to be used for name resolution.

o The upstream network provider is not the DDoS mitigation provider for some of these use cases. The use of anycast is not appropriate for this use case, in particular. It is safe to assume that for such deployments, the DOTS server(s) domain name is provided during the service subscription (i.e., manual/local configuration).

o Multiple DOTS clients may be enabled within a network (e.g., enterprise network). Automatic means to discover DOTS servers in a deterministic manner are interesting from an operational standpoint.

o Some of the use cases may involve a DOTS gateway that is responsible for forking requests received from DOTS clients to upstream DOTS servers or for selecting the appropriate DOTS server. Particularly, the use of anycast may simplify the operations within the enterprise network to discover a DOTS gateway, if the enterprise network is single-homed.

o Many use cases discussed in [I-D.ietf-dots-use-cases] do involve a CPE device. Multiple CPEs, connected to distinct network providers may even be considered. It is intuitive to leverage on existing mechanisms such as discovery using service resolution or



o A resolution mechanism based on straightforward Naming Authority Pointer (S-NAPTR) resource records in the Domain Name System (DNS).

o DNS Service Discovery.

o Discovery using DHCP Options.

o A mechanism based on anycast address for DOTS usage.

5. Discovery Procedure

A key point in the deployment of DOTS is the ability of network operators to be able to configure DOTS clients with the correct server information consistently. To accomplish this, operators will need a consistent set of ways in which DOTS clients can discover this information, and a consistent priority among these options. If some devices prefer manual configuration over DNS discovery, while others prefer DNS discovery over manual configuration, the result will be a process of "whack-a-mole", where the operator must find devices that are using the wrong DOTS server, determine how to ensure the devices are configured properly, and then reconfigure the device through the preferred method.

All DOTS clients MUST support at least one of the four mechanisms below to determine a DOTS server list. All DOTS clients SHOULD implement all four, or as many as are practical for any specific device, of these ways to discover DOTS servers, in order to facilitate the deployment of DOTS in large scale environments:

1. Explicit configuration:

* Local/Manual configuration: A DOTS client, will learn the DOTS server(s) by means of local or manual DOTS configuration (i.e., DOTS servers configured at the system level). Configuration discovered from a DOTS client application is considered as local configuration. An implementation may give the user an opportunity (e.g., by means of configuration file options or menu items) to specify DOTS server(s) for each address family. These MAY be specified either as IP addresses or the DNS name of a DOTS server. When only DOTS server’ IP addresses are configured, a reference identifier must also be configured for authentication purposes.

* Automatic configuration (e.g., DHCP, an automation system): The DOTS client attempts to discover DOTS server(s) names and/ or addresses from DHCP, as described in Section 9.



2. Service Resolution : The DOTS client attempts to discover DOTS server name(s) using service resolution, as specified in Section 7.

3. DNS SD: DNS Service Discovery. The DOTS client attempts to discover DOTS server name(s) using DNS service discovery, as specified in Section 8.

4. Anycast : Send DOTS request to establish a DOTS session with the assigned DOTS server anycast address for each combination of interface and address family.

Some of these mechanisms imply the use of DNS to resolve the IP address of the DOTS server, while others imply the IP address of the relevant DOTS server is obtained directly. Implementation options may vary on a per device basis, as some devices may not have DNS capabilities and/or proper configuration.

Clients will prefer information received from the discovery methods in the order listed.

On hosts with more than one interface or address family (IPv4/v6), the DOTS server discovery procedure has to be performed for each combination of interface and address family. A client MAY choose to perform the discovery procedure only for a desired interface/address combination if the client does not wish to discover a DOTS server for all combinations of interface and address family.

The above procedure MUST also be followed by a DOTS gateway.

6. Resolution

Once the DOTS client has retrieved client’s DNS domain or discovered the DOTS server name that needs to be resolved, an S-NAPTR lookup with ’DOTS’ application service and the desired protocol tag is made to obtain information necessary to connect to the authoritative DOTS server within the given domain.

This specification defines "DOTS" as an application service tag (Section 12.3.1) and "signal.udp" (Section 12.3.2), "signal.tcp" (Section 12.3.3), and "data.tcp" (Section 12.3.4) as application protocol tags.



In the example below, for domain ’example.net’, the resolution algorithm will result in IP address(es), port, tag and protocol tuples as follows:

example.net. IN NAPTR 100 10 "" DOTS:signal.udp "" signal.example.net. IN NAPTR 200 10 "" DOTS:signal.tcp "" signal.example.net. IN NAPTR 300 10 "" DOTS:data.tcp "" data.example.net.

signal.example.net. IN NAPTR 100 10 S DOTS:signal.udp "" _dots._signal._udp.example.net. IN NAPTR 200 10 S DOTS:signal.tcp "" _dots._signal._tcp.example.net.

data.example.net. IN NAPTR 100 10 S DOTS:data.tcp "" _dots._data._tcp.example.net.

_dots._signal._udp.example.net. IN SRV 0 0 5000 a.example.net.

_dots._signal._tcp.example.net. IN SRV 0 0 5001 a.example.net.

_dots._data._tcp.example.net. IN SRV 0 0 5002 a.example.net.

a.example.net. IN AAAA 2001:db8::1

+-------+----------+-------------+------+--------+ | Order | Protocol | IP address | Port | Tag | +-------+----------+-------------+------+--------+ | 1 | UDP | 2001:db8::1 | 5000 | Signal | | 2 | TCP | 2001:db8::1 | 5001 | Signal | | 3 | TCP | 2001:db8::1 | 5002 | Data | +-------+----------+-------------+------+--------+

If no DOTS-specific S-NAPTR records can be retrieved, the discovery procedure fails for this domain name (and the corresponding interface and IP protocol version). If more domain names are known, the discovery procedure MAY perform the corresponding S-NAPTR lookups immediately. However, before retrying a lookup that has failed, a DOTS client MUST wait a time period that is appropriate for the encountered error (e.g., NXDOMAIN, timeout, etc.).



7. Discovery using Service Resolution

This mechanism is performed in two steps:

1. A DNS domain name is retrieved for each combination of interface and address family.

2. Retrieved DNS domain names are then used for S-NAPTR lookups. Further DNS lookups may be necessary to determine DOTS server IP address(es).

7.1. Retrieving Domain Name

A DOTS client has to determine the domain in which it is located. The following section describes the means to obtain the domain name from DHCP. Other means of retrieving domain names may be used, which are outside the scope of this document, e.g., local configuration.

Implementations MAY allow the user to specify a default name that is used, if no specific name has been configured.

7.1.1. DHCP

DHCP can be used to determine the domain name related to an interface’s point of network attachment. Network operators may provide the domain name to be used for service discovery within an access network using DHCP. Sections 3.2 and 3.3 of [RFC5986] define DHCP IPv4 and IPv6 access network domain name options, OPTION_V4_ACCESS_DOMAIN and OPTION_V6_ACCESS_DOMAIN respectively, to identify a domain name that is suitable for service discovery within the access network.

For IPv4, the discovery procedure MUST request the access network domain name option in a Parameter Request List option, as described in [RFC2131]. [RFC2132] defines the DHCP IPv4 domain name option; while this option is less suitable, a client MAY request for it if the access network domain name defined in [RFC5986] is not available.

For IPv6, the discovery procedure MUST request for the access network domain name option in an Options Request Option (ORO) within an Information-request message, as described in [RFC3315].

If neither option can be retrieved the procedure fails for this interface. If a result can be retrieved it will be used as an input for S-NAPTR resolution discussed in Section 6.



8. DNS Service Discovery

DNS-based Service Discovery (DNS-SD) [RFC6763] and Multicast DNS (mDNS) [RFC6762] provide generic solutions for discovering services. DNS-SD/mDNS define a set of naming rules for certain DNS record types that they use for advertising and discovering services.

8.1. DNS-SD

Section 4.1 of [RFC6763] specifies that a service instance name in DNS-SD has the following structure:

<Instance> . <Service> . <Domain>

The <Domain> portion specifies the DNS sub-domain where the service instance is registered. It may be "local.", indicating the mDNS local domain, or it may be a conventional domain name such as "example.com.".

The <Service> portion of the DOTS service instance name MUST be "_dots._signal._udp" or "_dots._signal._tcp" or "_dots._data._tcp".

8.2. mDNS

A DOTS client can proactively discover DOTS servers being advertised in the site by multicasting a PTR query to one or all of the following:

o "_dots._signal._udp.local."

o "_dots._signal._tcp.local."

o "_dots._data._tcp.local."

A DOTS server can send out gratuitous multicast DNS answer packets whenever it starts up, wakes from sleep, or detects a change in network configuration. DOTS clients receive these gratuitous packets and cache information contained in it.

9. DHCP Options for DOTS

As reported in Section 1.7.2 of [RFC6125]:

"few certification authorities issue server certificates based on IP addresses, but preliminary evidence indicates that such certificates are a very small percentage (less than 1%) of issued certificates".



In order to allow for PKIX-based authentication between a DOTS client and server while accommodating for the current best practices for issuing certificates, this document allows for configuring names to DOTS clients. These names can be used for two purposes: to retrieve the list of IP addresses of a DOTS server or to be presented as a reference identifier for authentication purposes.

Defining the option to include a list of IP addresses would avoid a dependency on an underlying name resolution, but that design requires to also supply a name for PKIX-based authentication purposes.

9.1. DHCPv6 DOTS Options

9.1.1. Format of DOTS Reference Identifier Option

The DHCPv6 DOTS option is used to configure a name of the DOTS server. The format of this option is shown in Figure 2.

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_V6_DOTS | Option-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | dots-server-name (FQDN) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: DHCPv6 DOTS Reference Identifier option


o Option-code: OPTION_V6_DOTS_RI (TBA1, see Section 12.1) o Option-length: Length of the dots-server-name field in octets. o dots-server-name: A fully qualified domain name of the DOTS server. This field is formatted as specified in Section 8 of [RFC3315].

An example of the dots-server-name encoding is shown in Figure 3. This example conveys the FQDN "dots.example.com.".

+------+------+------+------+------+------+------+------+------+ | 0x04 | d | o | t | s | 0x07 | e | x | a | +------+------+------+------+------+------+------+------+------+ | m | p | l | e | 0x03 | c | o | m | 0x00 | +------+------+------+------+------+------+------+------+------+

Figure 3: An example of the dots-server-name encoding



9.1.2. Format Format of DOTS Address Option

The DHCPv6 DOTS option can be used to configure a list of IPv6 addresses of a DOTS server. The format of this option is shown in Figure 4.

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_V6_DOTS | Option-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | DOTS ipv6-address | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | DOTS ipv6-address | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: DHCPv6 DOTS Address option


o Option-code: OPTION_V6_DOTS_ADDRESS (TBA2, see Section 12.1) o Option-length: Length of the ’DOTS ipv6-address(es)’ field in octets. MUST be a multiple of 16. o DOTS ipv6-address: Includes one or more IPv6 addresses [RFC4291] of the DOTS server to be used by the DOTS client.

Note, IPv4-mapped IPv6 addresses (Section 2.5.5.2 of [RFC4291]) are allowed to be included in this option.

To return more than one DOTS servers to the requesting DHCPv6 client, the DHCPv6 server returns multiple instances of OPTION_V6_DOTS.


DHCP clients MAY request options OPTION_V6_DOTS_RI and OPTION_V6_DOTS_ADDRESS, as defined in [RFC3315], Sections 17.1.1, 18.1.1, 18.1.3, 18.1.4, 18.1.5, and 22.7. As a convenience to the reader, it is mentioned here that the DHCP client includes the requested option codes in the Option Request Option.



If the DHCP client receives more than one instance of OPTION_V6_DOTS_RI (resp. OPTION_V6_DOTS_ADDRESS) option, it MUST use only the first instance of that option.

If the DHCP client receives both OPTION_V6_DOTS_RI and OPTION_V6_DOTS_ADDRESS, the content of OPTION_V6_DOTS_RI is used as reference identifier for authentication purposes (e.g., PKIX [RFC6125]), while the addresses included in OPTION_V6_DOTS_ADDRESS are used to reach the DOTS server. In other words, the name conveyed in OPTION_V6_DOTS_RI MUST NOT be passed to underlying resolution library in the presence of OPTION_V6_DOTS_ADDRESS in a response.

If the DHCP client receives OPTION_V6_DOTS_RI only, but OPTION_V6_DOTS_RI option contains more than one name, as distinguished by the presence of multiple root labels, the DHCP client MUST use only the first name. Once the name is validated (Section 8 of [RFC3315]), the name is passed to a name resolution library. Moreover, that name is also used as a reference identifier for authentication purposes.

If the DHCP client receives OPTION_V6_DOTS_ADDRESS only, the address(es) included in OPTION_V6_DOTS_ADDRESS is used to reach the DOTS server. In addition, these addresses can be used as identifiers for authentication.

9.2. DHCPv4 DOTS Options

9.2.1. Format of DOTS Reference Identifier Option

The DHCPv4 DOTS option is used to configure a name of the DOTS server. The format of this option is illustrated in Figure 5.

Code Length DOTS server name +-----+-----+-----+-----+-----+-----+-----+-- | TBA | n | s1 | s2 | s3 | s4 | s5 | ... +-----+-----+-----+-----+-----+-----+-----+--

The values s1, s2, s3, etc. represent the domain name labels in the domain name encoding.

Figure 5: DHCPv4 DOTS Reference Identifier option


o Code: OPTION_V4_DOTS_RI (TBA3, see Section 12.2); o Length: Includes the length of the "DOTS server name" field in octets; the maximum length is 255 octets.



o DOTS server name: The domain name of the DOTS server. This field is formatted as specified in Section 8 of [RFC3315].

9.2.2. Format Format of DOTS Address Option

The DHCPv4 DOTS option can be used to configure a list of IPv4 addresses of a DOTS server. The format of this option is illustrated in Figure 6.

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | List-Length | List of | +-+-+-+-+-+-+-+-+ DOTS | / IPv4 Addresses / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- | List-Length | List of | | +-+-+-+-+-+-+-+-+ DOTS | | / IPv4 Addresses / | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . ... . optional +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | List-Length | List of | | +-+-+-+-+-+-+-+-+ DOTS | | / IPv4 Addresses / | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---

Figure 6: DHCPv4 DOTS Address option


o Code: OPTION_V4_DOTS_ADDRESS (TBA4, see Section 12.2); o Length: Length of all included data in octets. The minimum length is 5. o List-Length: Length of the "List of DOTS IPv4 Addresses" field in octets; MUST be a multiple of 4. o List of DOTS IPv4 Addresses: Contains one or more IPv4 addresses of the DOTS server to be used by the DOTS client. The format of this field is shown in Figure 7. o OPTION_V4_DOTS can include multiple lists of DOTS IPv4 addresses; each list is treated separately as it corresponds to a given DOTS server.

When several lists of DOTS IPv4 addresses are to be included, "List-Length" and "DOTS IPv4 Addresses" fields are repeated.



0 8 16 24 32 40 48 +-----+-----+-----+-----+-----+-----+-- | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-- IPv4 Address 1 IPv4 Address 2 ...

This format assumes that an IPv4 address is encoded as a1.a2.a3.a4.

Figure 7: Format of the List of DOTS IPv4 Addresses

OPTION_V4_DOTS is a concatenation-requiring option. As such, the mechanism specified in [RFC3396] MUST be used if OPTION_V4_DOTS exceeds the maximum DHCPv4 option size of 255 octets.


To discover a DOTS server, the DHCPv4 client MUST include both OPTION_V4_DOTS_RI and OPTION_V4_DOTS_ADDRESS in a Parameter Request List Option [RFC2132].

If the DHCP client receives more than one instance of OPTION_V4_DOTS_RI (resp. OPTION_V4_DOTS_ADDRESS) option, it MUST use only the first instance of that option.

If the DHCP client receives both OPTION_V4_DOTS_RI and OPTION_V4_DOTS_ADDRESS, the content of OPTION_V6_DOTS_RI is used as reference identifier for authentication purposes, while the addresses included in OPTION_V4_DOTS_ADDRESS are used to reach the DOTS server. In other words, the name conveyed in OPTION_V4_DOTS_RI MUST NOT be passed to underlying resolution library in the presence of OPTION_V4_DOTS_ADDRESS in a response.

If the DHCP client receives OPTION_V4_DOTS_RI only, but OPTION_V4_DOTS_RI option contains more than one name, as distinguished by the presence of multiple root labels, the DHCP client MUST use only the first name. Once the name is validated (Section 8 of [RFC3315]), the name is passed to a name resolution library. Moreover, that name is also used as a reference identifier for authentication purposes.

If the DHCP client receives OPTION_V4_DOTS_ADDRESS only, the address(es) included in OPTION_V4_DOTS_ADDRESS is used to reach the DOTS server. In addition, these addresses can be used as identifiers for authentication.



10. Anycast

IP anycast can also be used for DOTS service discovery. A packet sent to an anycast address is delivered to the ’topologically nearest’ network interface with the anycast address.

When a DOTS client requires DOTS services, it attempts to establish a signaling session with the assigned anycast address(es) defined in Sections 12.4 and 12.5. A DOTS server, that receives a DOTS request with an anycast address, SHOULD redirect the DOTS client to the appropriate DOTS unicast server(s) using the mechanism described in Section 5.5 of [I-D.ietf-dots-signal-channel], unless it is configured otherwise. Indeed, a DOTS server SHOULD be configurable to maintain all DOTS communications using anycast. DOTS redirect is not made mandatory because the use of anycast is not problematic for some deployment scenarios such as an enterprise network deploying one single DOTS gateway connected to one single network provider.

[I-D.boucadair-dots-multihoming] identifies a set of deployment schemes in which the use of anycast is not recommended.


DOTS-related security considerations are discussed in Section 4 of [I-D.ietf-dots-architecture] is to be considered. DOTS agents must authenticate each other using (D)TLS before a DOTS session is considered valid.

If the DOTS client is explicitly configured with DOTS server(s) then the DOTS client can also be explicitly configured with credentials to authenticate the DOTS server.

The CPE device acting as a DOTS client MAY use Bootstrapping Remote Secure Key Infrastructures (BRSKI) discussed in [I-D.ietf-anima-bootstrapping-keyinfra] to automatically bootstrap using the vendor installed X.509 certificate, in combination with a domain registrar provided by the upstream transit provider and vendor’s authorizing service. The CPE device authenticates to the upstream transit provider using the vendor installed X.509 certificate and the upstream transit provider validates the vendor installed certificate on the CPE device using the Manufacturer Authorized Signing Authority (MASA) service. If authentication is successful then the CPE device can request and get a voucher from the MASA service via the domain registrar. The voucher is signed by the MASA service and includes the upstream transit provider’s trust anchor certificate. The CPE device validates the signed voucher using the manufacturer installed trust anchor associated with the vendor’s selected MASA service and stores the upstream transit



provider’s trust anchor certificate. The CPE device then uses Enrollment over Secure Transport (EST) [RFC7030] for certificate enrollment (Section 3.8 in [I-D.ietf-anima-bootstrapping-keyinfra]). The DOTS client on the CPE device can authenticate to the DOTS server using the certificate provisioned by the EST server and the DOTS client can validate the DOTS server certificate using the upstream transit provider’s trust anchor certificate it had received in the voucher.

11.1. DHCP

The security considerations in [RFC2131] and [RFC3315] are to be considered.

11.2. Service Resolution

The primary attack against the methods described in Section 7 is one that would lead to impersonation of a DOTS server. An attacker could attempt to compromise the S-NAPTR resolution. The use of mutual authentication makes it difficult to redirect a DOTS client to an illegitimate DOTS server.

11.3. DNS Service Discovery

Since DNS-SD is just a specification for how to name and use records in the existing DNS system, it has no specific additional security requirements over and above those that already apply to DNS queries and DNS updates. For DNS queries, DNS Security Extensions (DNSSEC) [RFC4033] SHOULD be used where the authenticity of information is important. For DNS updates, secure updates [RFC2136][RFC3007] SHOULD generally be used to control which clients have permission to update DNS records.

For mDNS, in addition to what has been described above, a principal security threat is a security threat inherent to IP multicast routing and any application that runs on it. A rogue system can advertise that it is a DOTS server. Discovery of such rogue systems as DOTS servers, in itself, is not a security threat if the DOTS client authenticates the discovered DOTS servers.

11.4. Anycast

Anycast-related security considerations are discussed in [RFC4786] and [RFC7094].




IANA is requested to allocate the SRV service name of "_dots._signal" for DOTS signal channel over UDP or TCP, and the service name of "_dots._data" for DOTS data channel over TCP.

12.1. DHCPv6 Option

IANA is requested to assign the following new DHCPv6 Option Code in the registry maintained in http://www.iana.org/assignments/ dhcpv6-parameters:

Option Name Value ---------------------- ----- OPTION_V6_DOTS_RI TBA1 OPTION_V6_DOTS_ADDRESS TBA2

12.2. DHCPv4 Option

IANA is requested to assign the following new DHCPv4 Option Code in the registry maintained in http://www.iana.org/assignments/bootp- dhcp-parameters/:

Option Name Value Data length Meaning ---------------------- ----- ------------ --------------------------- OPTION_V4_DOTS_RI TBA3 Variable; Includes the name of the the maximum DOTS server. length is 255 octets. OPTION_V4_DOTS_ADDRESS TBA4 Variable; Includes one or multiple the minimum lists of DOTS IP addresses; length is 5. each list is treated as a separate DOTS server.

12.3. Application Service & Application Protocol Tags

This document requests IANA to make the following allocations from the registry available at: https://www.iana.org/assignments/s-naptr- parameters/s-naptr-parameters.xhtml.

12.3.1. DOTS Application Service Tag Registration

o Application Protocol Tag: DOTS






12.3.2. signal.udp Application Protocol Tag Registration

o Application Protocol Tag: signal.udp




12.3.3. signal.tcp Application Protocol Tag Registration

o Application Protocol Tag: signal.tcp




12.3.4. data.tcp Application Protocol Tag Registration

o Application Protocol Tag: data.tcp




12.4. IPv4 Anycast

IANA has assigned a single IPv4 address from the 192.0.0.0/24 prefix and registered it in the "IANA IPv4 Special-Purpose Address Registry" [RFC6890].




12.5. IPv6 Anycast

IANA has assigned a single IPv6 address from the 2001:0000::/23 prefix and registered it in the "IANA IPv6 Special-Purpose Address Registry" [RFC6890].



Thanks to Brian Carpenter for the review of the BRSKI text.

Many thanks to Russ White for the review, comments, and text contribution.



14. References


[I-D.ietf-dots-architecture] Mortensen, A., Andreasen, F., K, R., [email protected], c., Compton, R., and N. Teague, "Distributed-Denial-of-Service Open Threat Signaling (DOTS) Architecture", draft-ietf-dots- architecture-07 (work in progress), September 2018.


[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, DOI 10.17487/RFC2131, March 1997, <https://www.rfc-editor.org/info/rfc2131>.

[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997, <https://www.rfc-editor.org/info/rfc2132>.

[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 2003, <https://www.rfc-editor.org/info/rfc3315>.

[RFC3396] Lemon, T. and S. Cheshire, "Encoding Long Options in the Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396, DOI 10.17487/RFC3396, November 2002, <https://www.rfc-editor.org/info/rfc3396>.

[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application Service Location Using SRV RRs and the Dynamic Delegation Discovery Service (DDDS)", RFC 3958, DOI 10.17487/RFC3958, January 2005, <https://www.rfc-editor.org/info/rfc3958>.

[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006, <https://www.rfc-editor.org/info/rfc4291>.

[RFC5986] Thomson, M. and J. Winterbottom, "Discovering the Local Location Information Server (LIS)", RFC 5986, DOI 10.17487/RFC5986, September 2010, <https://www.rfc-editor.org/info/rfc5986>.



[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, DOI 10.17487/RFC6762, February 2013, <https://www.rfc-editor.org/info/rfc6762>.

[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, <https://www.rfc-editor.org/info/rfc6763>.

[RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, "Special-Purpose IP Address Registries", BCP 153, RFC 6890, DOI 10.17487/RFC6890, April 2013, <https://www.rfc-editor.org/info/rfc6890>.



[I-D.boucadair-dots-multihoming] Boucadair, M. and R. K, "Multi-homing Deployment Considerations for Distributed-Denial-of-Service Open Threat Signaling (DOTS)", draft-boucadair-dots- multihoming-03 (work in progress), April 2018.

[I-D.ietf-anima-bootstrapping-keyinfra] Pritikin, M., Richardson, M., Behringer, M., Bjarnason, S., and K. Watsen, "Bootstrapping Remote Secure Key Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping- keyinfra-16 (work in progress), June 2018.

[I-D.ietf-dots-signal-channel] K, R., Boucadair, M., Patil, P., Mortensen, A., and N. Teague, "Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification", draft- ietf-dots-signal-channel-25 (work in progress), September 2018.


[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, DOI 10.17487/RFC2136, April 1997, <https://www.rfc-editor.org/info/rfc2136>.



[RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic Update", RFC 3007, DOI 10.17487/RFC3007, November 2000, <https://www.rfc-editor.org/info/rfc3007>.

[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, DOI 10.17487/RFC4033, March 2005, <https://www.rfc-editor.org/info/rfc4033>.


[RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786, December 2006, <https://www.rfc-editor.org/info/rfc4786>.

[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March 2011, <https://www.rfc-editor.org/info/rfc6125>.

[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed., "Enrollment over Secure Transport", RFC 7030, DOI 10.17487/RFC7030, October 2013, <https://www.rfc-editor.org/info/rfc7030>.

[RFC7094] McPherson, D., Oran, D., Thaler, D., and E. Osterweil, "Architectural Considerations of IP Anycast", RFC 7094, DOI 10.17487/RFC7094, January 2014, <https://www.rfc-editor.org/info/rfc7094>.





DOTS J. FrancoisInternet-Draft InriaIntended status: Standards Track A. LahmadiExpires: November 4, 2017 University of Lorraine - LORIA M. Davids G. Moura SIDN Labs May 3, 2017

IPv6 DOTS Signal Option draft-francois-dots-ipv6-signal-option-02

Abstract

DOTS client signal using original signal communication channel can expect service degradation and even service disruption as any other service over Internet but in more severe conditions because the signal may have to be transmitted over congested paths due to the denial-of-service attack.

This document specifies a fall-back asynchronous mechanism using an intermediate agent to store DOTS signal information during a limited period of time. This mechanism allows a DOTS server to request a signal information stored by a DOTS client when no heartbeat is received from the DOTS client. This intermediate agent called DOTS Signal Repository have to be connected to the DOTS client and server independently. The repository must be located and/or reached through one or multiple network paths, preferably as most as possible disjoint from regular signal channel, in order to increase its reachability. The document introduces a set of support protocols to build the asynchronous communication between the DOTS cient, server and the repository.

Status of This Memo




Francois, et al. Expires November 4, 2017 [Page 1]

Internet-Draft IPv6 DOTS Signal Option May 2017

This Internet-Draft will expire on November 4, 2017.

Copyright Notice



Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. Asynchronous DOTS signaling . . . . . . . . . . . . . . . . . 4 2.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Architecture . . . . . . . . . . . . . . . . . . . . . . 5 2.3. Asynchronous process . . . . . . . . . . . . . . . . . . 5 2.4. Protocol requirements . . . . . . . . . . . . . . . . . . 6 3. DOTS Signal Repository . . . . . . . . . . . . . . . . . . . 7 4. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Between DSR and DOTS server . . . . . . . . . . . . . . . 7 4.2. Between DSR and DOTS client . . . . . . . . . . . . . . . 7 4.2.1. Opportunistic DOTS signaling . . . . . . . . . . . . 8 4.2.1.1. Hop-by-Hop option encoding . . . . . . . . . . . 9 4.2.1.2. DOTS signal Option attributes . . . . . . . . . . 10 4.2.1.3. Example . . . . . . . . . . . . . . . . . . . . . 11 4.2.1.4. Option Processing . . . . . . . . . . . . . . . . 12 4.2.1.5. Deployment considerations . . . . . . . . . . . . 14 4.2.1.6. Impact on existing IP layer implementations . . . 15 4.2.2. IPv6 SRH . . . . . . . . . . . . . . . . . . . . . . 15 5. Security Considerations . . . . . . . . . . . . . . . . . . . 15 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.1. Normative References . . . . . . . . . . . . . . . . . . 17 8.2. Informative References . . . . . . . . . . . . . . . . . 17 Appendix A. Additional Stuff . . . . . . . . . . . . . . . . . . 18 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 19



1. Introduction

1.1. Overview

A distributed denial-of-service (DDoS) attack aims at rendering machines or network resources unavailable. These attacks have grown in frequency, intensity and target diversity [I-D.ietf-dots-requirements]. Moreover, several protocols have been utilized to amplify the intensity of the attacks [kuhrer2014exit], peaking at several hundred gigabits per second.

DDoS Open Threat Signaling (DOTS) aims at defining a common and open protocol to signal DDoS attacks to facilitate a coordinated response to these attacks. This document specifies an asynchronous signaling method that MAY be used between a DOTS client and server instead of relying on purely synchronous communication as specified in [I-D.ietf-dots-signal-channel]. Indeed initial signaling should be done in real-time through connections between DOTS clients and severs such that a client can forward signal information as soon as the attack is detected. However, the signaling messages may have to be forwarded through paths impacted by the attack itself, i.e. highly congested. Asynchronous signaling in this document is an additional mechanism which MAY propagate signal information in a less reactive manner due to the use of an asynchronous communication channel but through alternative paths in the network. It increases the reachability of the DOTS server which will then in charge of requesting the mitigation.

The proposed mechanism constitutes an additional signaling channel but MUST NOT replace the original signaling channel used between DOTS client and servers as the one defined in [I-D.ietf-dots-signal-channel].

To perform asynchronous communication, this document introduces DOTS Signals Repository (DSR) which represents datastores where DOTS clients can send signal information. This information is then stored and the DOTS server can request it. In addition to provide a general process for achieving asynchronous signaling, this document introduces also a set of protocols which can support it.

1.2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

The terms DOTS client, DOTS server, DOTS gateway, DOTS agents refers to the terminology introduced in [I-D.ietf-dots-architecture].



The following terms are introduced:

o DSR (DOTS signal repository): intermediate agent able to store signal from clients during a limited period of time and which can be requested by DOTS servers.

o Opportunistic DOTS signal: an IPv6 packet containing the signaling attributes of an attack within the Hop-by-Hop extension header. The purpose is the same as the DOTS signal. It is used to request help for mitigating the attack.

o DOTS opportunistic-capable router: a router with the capacity to decode the opportunistic DOTS signal and re-embed such an information in other IPv6 packets.

o All DOTS opportunistic-capable agents are defined as the DOTS agents supporting the opportunistic DOTS signal processing.

2. Asynchronous DOTS signaling

2.1. Motivation

The traffic generated by a DDoS can be characterized according to various parameters, such as the layer (IP/ICMP or application), maximum and instant throughput, among others. Regardless its nature, we assume that for most cases, a DOTS client will be able to signal back one or few messages, during the attack, to the DOTS phase.

We have the same behavior in other DDoS attacks. For instance, on November 30th and December 1st, 2015, the Root DNS system was hit by an application layer (DNS) attack [rootops-ddos]. Each one of the 13 root server letters (A-M) was hit by attacks peaking at 5 million queries per second. By utilizing the RIPE Atlas DNSMON infrastructure, we can see that during the DDoS attacks, most of the root server letters remained reachable and able to respond to the DNS request sent by the probes employed by the DNSMON [ripe-dnsmon-ddos]. Few letters, however, had a packet loss rate of more than 99%. The DNSMON probes, however, experience mostly delays in their DNS requests instead.

As regular signaling from the DOTS client to the DOTS server or the DOTS gateway might be affected by the attack traffic, it is important to maximize the delivering success of the signals by using alternative packets and/or paths to deliver it. As a result, it forces to have intermediate agents, DSRs, able to catch DOTS signals delivered through those auxiliary mechanisms. However, those agents MUST not always forward DOTS signal to the server in order to limit the induced overhead. Only if the regular signal is not received by



the server, retrieving the signal from the DSRs is required, which has thus initiated by the DOTS server itself.

2.2. Architecture

DSR (DOTS Signal Repository) are additional REQUIRED datastores. They are integrated in the DOTS architecture [I-D.ietf-dots-architecture]as highlighted in Figure 1. (1) refers to the regular signaling. (2) and (3) refers to the proposed auxiliary mechanism. As shown in this figure, DSRs act as synchronizing agent where the DOTS client drops signal information (2) (attack details). On the contrary, the server will retrieve this information (3).

+-----------+ +-------------+ | Mitigator | ˜˜˜˜˜˜˜˜˜˜ | DOTS Server |˜˜˜˜+ +-----------+ +-------------+ |(3) ^ v | +----------------+ (1)| | DOTS Signal | | | Repository | | +----------------+ | ^ +---------------+ +-------------+ |(2) | Attack Target | ˜˜˜˜˜˜ | DOTS Client |˜˜˜˜+ +---------------+ +-------------+

Figure 1: Asynchronous signaling

2.3. Asynchronous process

This section describes the process of asynchronous DOTS signal processing. In Figure Figure 1, there are two main communication channels which are not synchronized:

o Between DOTS client and DSR: the client sends DOTS signal information when a condition is satisfied. The condition MUST be configured by the user but SHOULD be linked to information provided by Attack target. For instance, when an attack is detected, the client connects to DOTS server and in parallel sends signal to one or more DSRs.



o Between DOTS server and DSR: the server will retrieve signal information when a specific condition occurs. Such a condition is linked with the probable occurrence of an attack. The server can infer this condition when the client is not responsive anymore. In [I-D.ietf-dots-signal-channel], an heartbeat mechanism is defined. Hence, when no heartbeat is received from the client, the server MUST try to get signal information by the asynchronous communication channel.

Each communication channel can implement its own protocol. They are NOT REQUIRED to be the same.

We have to note that the client condition to provide signals to the DSR can be weaker than regular synchronous signaling between DOTS client and server. Indeed, a client can signal to the DSR some suspect activities for which no mitigation is required yet. However, when the supposed attack is stronger provoking client disruption, the latter is not able to provide any type of signaling anymore and the server can thus retrieve information on prior stored signals.

2.4. Protocol requirements

DOTS signaling requirements are documented in [I-D.ietf-dots-requirements].

GEN-003 (Bidirectionality) requires that signal channel MUST enable asynchronous communications between DOTS agent by allowing unsolicited messages. Asynchronous signaling described in the current document allows DOTS client to provide signals, which can be retrieved later by DOTS server(s).

Because of this mechanism, there are requirements which are not supported: OP-002 (Session Health Monitoring), OP-003 (Session Redirection). Therefore, the fall-back asynchronous DOTS signaling is an additionnal mechanism and MUST NOT replace regular signaling as described in [I-D.ietf-dots-signal-channel].

It is particularly designed to fulfill GEN-002 (Resilience and Robustness) by increasing the signal delivery success even under the severely constrained network conditions imposed by particular attack traffic.

In addition, the fall-back asynchronous DOTS signal MUST specify a TTL (Time-to-Live) used by DSRs to store received signal in a limited period of time. It is different from mitigation lifetime but MUST be lower or equals.



3. DOTS Signal Repository

DSRs have to be deployed and distributed in order to enhance its reachability by the DOTS client. It is NOT REQUIRED that all DOTS agents use the same set of DSRs and a DOTS client and server SHOULD define their own set regarding their particular context, e.g. the network topology. The Data channel [I-D.ietf-dots-data-channel] between client and server MUST be used to configure it. As an example in the case of the inter-domain scenario, the DOTS server can inform the DOTS client to use DSRs scattered in multiple domains.

There is no restriction on the environment where DSRs can be deployed. Two types of DSRs are mainly considered:

o Routers: they have low capacity to process and store received signals but they are well distributed by nature in the network.

o Servers or stations: they provide higher computational power and storage but are less distributed

Selection of protocols to use for asynchronous signaling MUST take into account those specificities.

4. Protocol

4.1. Between DSR and DOTS server

To retrieve signals, the DOTS server MUST request the DSRs. Standard protocols can be used. Requests from the DOTS server MUST specify a client identifier and the DSRs returns all stored signal related to this client. The protocol MUST provide integrity and authenticity and SHOULD guarantee confidentiality. To limit entailed overhead lightweight protocol SHOULD be used. COAP [RFC7252] over DTLS [RFC6347] is RECOMMENDED when DSRs are servers. In the case of routers acting as DSR, network management protocol such as SNMP [RFC1157] or NETCONF [RFC6241] SHOULD be leveraged.

4.2. Between DSR and DOTS client

The signal sent by the DOTS client to the DSR is more prone to be affected by attack traffic due to its proximity to the attack victim. Similar protocol as between DSR and DOTS server can be used but it is RECOMMENDED to convey the signal over multiple paths to increase the reachability sucess



This document introduces two mechanisms to deliver the signal from the DOTS client to the DSR: IPv6 opportunistic signaling using Hop- by-Hop Option header; source routing using IPv6 Segment Routing Header (SRH).

4.2.1. Opportunistic DOTS signaling

This section specifies a signalling mechanism that instead of designing a new application-layer protocol, it utilizes the IPv6 Hop- by-Hop header [RFC2460]. This header SHOULD be processed by intermediate devices and it MUST be the first header in IPv6 extension headers [RFC7045].

In such a particular scenario, DSRs are intermediate routers capable of processing the option. DOTS server MAY also receive IPV6 packets with the Hop-by-Hop option and could thus process it directly. It is till considered as asynchronous since the server MAY NOT receive the initial packet emitted by the client but a copy of the signal in another packet (done by an intermediate DSR/router). Otherwise, it MUST connect to the DSR (section Section 4.1)

The new option containing the attributes of the signalling message is included in an opportunistic way in available IPv6 packets leaving a network element. The DOTS client will thus embed the signalling attributes into outgoing IPv6 packets not necessarily going to the DOTS server. Intermediate routers receiving such a packet will examine it and embed the same information into other IPv6 packets. domain in this opportunistic way to increase the probability that such a packet will be finally forwarded to a DOTS gateway or Server, but also in controlled way to avoid that the mechanism is exploited for a malicious purposes.

Only the Hop-by-Hop options header allows such behavior and using Destination options header is not enough to make the DOTS signal going through the network in an opportunistic way. Each network element recognizing this new option will select the best fitted IPv6 packets to deliver the signal to the DOTS DSRs. For this reason the Hop-by-Hop header option is essential to make such behavior compared to other existing IPv6 extension headers [RFC6564].

The goal is to provide an efficient mechanism where nodes in a IPv6 network facing a DDoS attack can deliver a DOTS signal message sent by a DOTS client to the DOTS server. The specified mechanism does not generate transport packets to carry the DOST signal message but it only relies on existing IPv6 packets in the network to include inside them a hop-by-hop extension header which contains an encoded DOTS signal message. The solution defines a new IPv6 Hop-by-Hop header option with the semantic that the network node SHOULD include



the option content within one or multiple outgoing IPv6 packets available in that network node.

4.2.1.1. Hop-by-Hop option encoding

According to [RFC2460], options encoded into the IPv6 Hop-by-Hop header are formatted as Type-Length-Values (TLVs). The option for opportunistic DOTS signal is thus defined as described in Figure 2

0 7 15 22 31 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option type |Option Data Len| DOTS Signal Attribute[1] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DOTS Signal Attribute[2] | ... | DOTS Signal Attribute[n] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: Hop-by-Hop option encoding

The first byte defines the Hop-by-Hop Option type number allocated to the DOTS opportunistic signalling. This number is not yet fixed but the first three bits MUST be set to 0. The first two zero bits indicate that routers which cannot handle the DOTS signal option will continue to process other options. The third 0 bit means that the option processing will not change the packet’s final destination [RFC2460].

The second byte contains the length of the option content. The content of the DOTS Signal option is a variable-length field that contains one or more type-length-values (TLV) encoded DOTS signal attributes, and has the format described in Figure 3.

0 7 15 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Attr Type | Attr Data Len | Attr Data ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: Hop-by-Hop option encoding

The Attr Type is 8-bit identifier of a DOTS signal attribute.

The Attr Data Len is 8-bit unsigned integer which is the length of Attr Data in bytes.

The Attr Data is variable-length field that contains the data of the attribute.



Since using TLVs in Hop-by-Hop options is known to be a factor of attacks [I-D.krishnan-ipv6-hopbyhop], DOTS attributes are encoded with fixed length when possible.

4.2.1.2. DOTS signal Option attributes

The first attribute embedded into the opportunistic DOTS signal is a TTL (Time-to-Live) field which indicates the maximum number of retransmission of the signal into another IPv6 packets until it MUST be discarded. Remaining attributes are similar to the header fields described in [I-D.ietf-dots-signal-channel] used to convey a DOTS signal through a HTTP POST.

The sequence of attributes to be inserted within the header MUST start with fixed-length attributes which are defined in the following order:

o TTL: Time-to-Live. This is a mandatory attribute encoded in one byte.

o Flags: one byte is reserved for flags. The first bit indicates the type of the IP address of the host: 0 for IPv4, 1 for IPv6. The second bit indicate if the protocol to use is TCP (1) or UDP (0). The third bit indicates if the message is signed. The remaining bit are not used yet.

o host: the IP address of the DOTS server where the signal option SHOULD be delivered. Depending on the flags, this field is encoded in 4 or 16 bytes.

o port: the listening port of the DOTS server. It is encoded in 2 bytes.

The remaining attributes MUST be TLV encoded, and they are defined in the following order:

o policy-id: defined in [I-D.ietf-dots-signal-channel].

o target-ip: defined in [I-D.ietf-dots-signal-channel]. However, each address or prefix is encoded in its own TLV element. The distinction between IPv4 and IPv6 is done over the length of the value.

o target-port: defined in [I-D.ietf-dots-signal-channel]. However, each target port is encoded in its own TLV element.

o target-protocol: defined in [I-D.ietf-dots-signal-channel] However each target protocol is encoded in its own TLV element.



o lifetime (lt): lifetime of the mitigation request defined in [I-D.ietf-dots-signal-channel]

The encoded attributes MUST be included in the option header in the order defined above.

Table 1 provides the value of types that are used by the TLV encoded attributes.

+-----------------+-------+ | Attribute type | Value | +-----------------+-------+ | policy-id | 0 | | target-ip | 1 | | target-port | 2 | | target-protocol | 3 | | lifetime | 4 | +-----------------+-------+

Table 1: TLV encoded attributes types

4.2.1.3. Example

Following is an example of an encoded Hop-by-Hop Option header to signal that a web service is under attack.

0 7 15 22 31 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next header | Hdr Ext Len=6 | TTL=128 | Flags=IPv4,TCP| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | host=192.0.2.1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | port=443 | A. type=policy| Att Data Len=2| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 143 | Attr. type=ip| Att Data Len=4| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 192.0.2.20 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Attr. type=ip |Att Data Len=16| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + + | | + + | 2001:db8:6401::1 | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Attr. type=port| Att Data Len=2| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



| 8080 |Attr. type=port| Att Data Len=2| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 443 |Attr.type=proto| Att Data Len=2| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TCP | Attr. type=lt | Att Data Len=2| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 600 | 1 | Opt Data Len=0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: Example of Hop-by-Hop DOTS signal encoding

In the previous example, the message is not signed and terminates with padding. If it is the case, then the signature MUST BE added at the end such that the integrity and authenticity can be checked by the DOTS server or gateway. The TTL attributes MUST be excluded from the signature calculation.

4.2.1.4. Option Processing

4.2.1.4.1. Opportunistic DOTS signal initialization by a DOTS client

When a DOTS client needs to inform the DOTS server that it is under attack, it firstly makes a connection attempt and applies the mechanisms described in [I-D.ietf-dots-signal-channel].

In addition, it MAY activates an opportunistic mechanism to include the Hop-by-Hop header option specified in this document in one or multiple available IPv6 packets leaving the node. Because the DOTS client location is independent of the signalling, it can be positionned in a part of the network where there is no passing-by traffic which can serve for opportunistic signalling. DOTS client MAY also create and emit IPv6 datagrams without payload but with the signal encoded in the Hop-by-Hop option header.

Otherwise, the selection of packets has to be configured a priori. The configuration is composed of a sequence of rules defined in a hierarchical order such that they are triggered in a sequential manner.

The selection of packets has to be configured a priori. The configuration is composed of a sequence of rules defined in a hierarchical order such that they are triggered in a sequential manner.

Each rule is defined by:

o a set of filters over the IPv6 packet headers. Only packets matching those filters are selected for opportunistic signalling.



For instance, only packets heading to a given subnetwork or to specific address close to a DOTS server can be selected to increase the chance to reach the latter.

o a ratio to select only a proportion of packets matching the filters in order to limit the induced overhead of the opportunistic signalling.

o a timeout until the rule is active and selected IPv6 packets embed the DOTS opportunistic signal.

The objective is to apply each ordered rule after another according to their timeouts. The first rule is triggered immediately after the opportunistic signalling is activated.

In all cases (embedding information into an exsiting packet or creating an new pakket with no payload), the client MUST avoid fragmentation.

Although the definition of rules MUST be configured by the user. It is RECOMMENDED to order them inversely related to the number of packets that would be selected. This can be approximated regarding the definition of filters. The core idea is to benefit from the first instants of the attack before losing connectivity by using a maximum number of outgoing packets to include the DOTS signalling option. It is thus RECOMMENDED to define the first as matching all IPv6 packets with a ratio equals one to rapidly disseminate the information but with a short timeout to limit the implied overhead.

Here is the an example of rules:

1. all outgoing IPv6 packets with a 10 second timeout

2. all outgoing IPv6 packets with a ratio of 10% and a 1 minute timeout

3. all outgoing multicast IPv6 packets with a ratio of 10% and a 1 minute timeout

4. all outgoing IPv6 packets heading to the DOTS server with a ratio of 100% and a one hour timeout

4.2.1.4.2. Processing by a non DOTS opportunistic-capable router

When receiving an opportunistic DOTS signal encoded in a IPv6 packet, a non DOT opportunistic capable router simply skips the Hop-by-Hop option and continue the normal processing of the IPv6 packet because the option type MUST start with three zero bits.



4.2.1.4.3. Processing by a DOTS opportunistic-capable router

A DOTS opportunistic-capable router MUST store DOTS signalling information whose it is aware of. If a router processes an IPv6 DOTS opportunistic signal and supports this option, it first checks if it has already stored the associated information. In that case, the router simply skips the option and continues the normal processing otherwise it stores the encoded information in order to embed it again in other IPv6 packets similarly to the DOTS client. Hence, a set of rules are also defined in advance and are triggered upon the reception of a new opportunistic DOTS signal. Once all rule have been applied, signalling information MUST be discarded by the router. When embedding the information into other IPv6 packets, the router MUST decrease the TTL by one since opportunistic signalling does not prevent loops in the dissemination of signalling.

4.2.1.4.4. Processing by a DOTS opportunistic-capable gateway

If a DOTS gateway has DOTS capabilities, it will apply the same strategy as a DOTS client by making attempts of direct connections to the DOST server and in addition it inserts the Hop-by-Hop header DOTS signalling option in leaving IPv6 packets using the strategy specified above.

4.2.1.4.5. Processing by a DOTS opportunistic-capable server

When the IP layer of the host where the DOTS server is running receives an IPv6 packet carrying a Hop-by-Hop DOTS signal option header it MUST extracts the content of the option and provides the attributes data to the server program.

4.2.1.5. Deployment considerations

This mechanism will be potentially used by networks with IPv6 capable elements and requires that of IPv6 traffic exist in the network during the attack. The existing IPv6 traffic to be used could be of any type from management or user levels. It is also important to emphasize that while our mechanism utilizes an IPv6 header field, it can also be used to signal IPv4 attacks as well - given that the network devices are dual stacked.

IPv6 extension headers are often rate-limited or dropped entirely. To be able to use the mechanism specified in this document, network operators need to avoid discarding packets or ignoring the processing of the hop-by-hop option on their deployed network elements. However, instead of dropping or ignoring packets with hop-by-hop option carrying DOTS signal, they need to assign these packets to slow forwarding path, and be processed by the router’s CPU. This



behavior will not affect the performance of the network devices since the network is already facing a DDoS attack and fast forwarding paths are saturated by the attacker traffic.

If the DOTS server, gateway and the client are located in the same administrative domain, marking the IPv6 packets with the proposed hop-by-hop header option could be done in a straight forward way, while considering that an agreement exists inside the domain to avoid dropping or rate limiting of IPv6 extension headers as described above. The proposed mechanism becomes less practical and difficult to deploy when the DOST server is running on the Internet. In such scenario, the mechanism could be used in the intra-domain part to deliver the hop-by-hop option carrying the DOTS signal until it reaches a DOTS gateway located in the same domain as the client, then the gateway will apply mechanisms provided by the DOTS transport protocol [I-D.ietf-dots-signal-channel] to inform the server running on Internet about the attack. This deployment scenario requires that at least one DOTS gateway is deployed in the same domain than the DOTS client.

4.2.1.6. Impact on existing IP layer implementations

For this option to be applicable within an IP system, it requires modifications to existing IP layer implementation. At DOTS capable nodes (client, gateway and server), it requires a service interface used by upper-layer protocols and application programs to ask the IP layer to insert and listen to the Hop-by-Hop header option in IPv6 packets. A DOTS client invokes the service interface to insert the option, A DOTS gateway invokes the service interface for listening and inserting the option, and finally a DOTS server only invokes the service interface to listen to the DOTS signalling option.

Intermediate nodes (routers or middle boxes) IP layer needs to be extended to perform processing of the new Hop-by-Hop header option. They mainly parse the first host attribute of the option and make a selection of a leaving IPv6 packet where the option will be inserted.

Every node inserting the new proposed Hop-by-Hop option SHOULD only select IPv6 packets with enough left space to avoid fragmentation.

4.2.2. IPv6 SRH

DOTS signalling may be carried using IPv6 source routing header. Details will be provided in a later version of this document.




Any IPv6 header option could be used by an attacker to create an attack on the routers and intermediate boxes that process packets containing the option. The proposed IPv6 option in this document MAY be abused by an attacker to create a covert channel at the IP layer where data is hidden inside the content of the option [RFC6564]. However, this attack is not specific to the proposed option and it is a known issue of IPv6 header extensions and options. The option MAY also be used by an attacker to forge or modify opportunistic DOTS signal leading to trigger additional processing on intermediate nodes and DOTS servers.

However the proposed option should be only initiated by a DOTS client and information embedded in new IPv6 messages by opportunistic DOTS capable routers. Defining proper policies to filter all messages with this option set and originated from other nodes would limit security issues since these DOTS opportunistic-capable agents SHOULD be trustworhy.

In addition, the message MAY be signed using techniques to enforce authenticity and integrity over the opportunistic DOTS signal channel. The signalling message specification includes a flag to indicate if the message is signed by the choice of the signature algorithm is let to the users. This signature has to be computed by the DOTS opportunistic-capable client and checked by the DOTS opportunistic-capable gateway or router. Hence, intermediate routers MUST NOT modify the message and its signature except the TTL, which so has not be considered during the signature computation.

Assuming a compromised router, the attacker could nevertheless replay the message or increase the TTL but thanks to the unique policy-id all intermediate-DOTS capable router will drop such messages and thus limiting their forwarding in the network.

Besides, an attacker can also listen opportunistic DOTS signals to monitor the impact of its own attack. These considerations are not specific to the proposed option and supposes that the attacker is able to compromise intermediate routers.


This draft defines a new IPv6 hop-by-hop option[RFC2460].This requires an IANA RFC3692-style update of:http://www.iana.org/ assignments/ipv6-parameters/ipv6-parameters.xhtml and ultimately the assignment of a new hop-by-hop option according to the guidelines described in [RFC5237].

7. Acknowledgements



This work is partly funded by FLAMINGO, a Network of Excellence Seventh Framework Programme.

8. References


[I-D.ietf-dots-architecture] Mortensen, A., Andreasen, F., Reddy, T., [email protected], c., Compton, R., and N. Teague, "Distributed-Denial-of-Service Open Threat Signaling (DOTS) Architecture", draft-ietf-dots- architecture-01 (work in progress), October 2016.

[I-D.ietf-dots-data-channel] Reddy, T., Boucadair, M., Nishizuka, K., Xia, L., Patil, P., Mortensen, A., and N. Teague, "Distributed Denial-of- Service Open Threat Signaling (DOTS) Data Channel", draft- ietf-dots-data-channel-00 (work in progress), April 2017.

[I-D.ietf-dots-requirements] Mortensen, A., Moskowitz, R., and T. Reddy, "Distributed Denial of Service (DDoS) Open Threat Signaling Requirements", draft-ietf-dots-requirements-04 (work in progress), March 2017.

[I-D.ietf-dots-signal-channel] Reddy, T., Boucadair, M., Patil, P., Mortensen, A., and N. Teague, "Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel", draft-ietf-dots-signal- channel-01 (work in progress), April 2017.

[I-D.krishnan-ipv6-hopbyhop] Krishnan, S., "The case against Hop-by-Hop options", draft-krishnan-ipv6-hopbyhop-05 (work in progress), October 2010.


[RFC1157] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple Network Management Protocol (SNMP)", RFC 1157, DOI 10.17487/RFC1157, May 1990, <http://www.rfc-editor.org/info/rfc1157>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>.



[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, December 1998, <http://www.rfc-editor.org/info/rfc2460>.

[RFC5237] Arkko, J. and S. Bradner, "IANA Allocation Guidelines for the Protocol Field", BCP 37, RFC 5237, DOI 10.17487/ RFC5237, February 2008, <http://www.rfc-editor.org/info/rfc5237>.

[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, <http://www.rfc-editor.org/info/rfc6241>.

[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012, <http://www.rfc-editor.org/info/rfc6347>.

[RFC6564] Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and M. Bhatia, "A Uniform Format for IPv6 Extension Headers", RFC 6564, DOI 10.17487/RFC6564, April 2012, <http://www.rfc-editor.org/info/rfc6564>.

[RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing of IPv6 Extension Headers", RFC 7045, DOI 10.17487/ RFC7045, December 2013, <http://www.rfc-editor.org/info/rfc7045>.

[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/ RFC7252, June 2014, <http://www.rfc-editor.org/info/rfc7252>.

[kuhrer2014exit] M. Kuhrer, T. Hupperich, C. Rossow, T. Holz, "Exit from Hell? Reducing the Impact of Amplification DDoS Attacks", USENIX Security Symposium 23rd, 2014.

[ripe-dnsmon-ddos] RIPE, "NCC DNS Monitoring Service (DNSMON)", <https:// atlas.ripe.net/dnsmon/>.

[rootops-ddos] rootops., "Events of 2015-11-30", 2015, <http://root-servers.org/news/events-of-20151130.txt>.

Appendix A. Additional Stuff



This becomes an Appendix.


Jerome Francois Inria 615 rue du jardin botanique Villers-les-Nancy 54600 FR

Phone: +33 3 83 59 30 66 Email: [email protected]

Abdelkader Lahmadi University of Lorraine - LORIA 615 rue du jardin botanique Villers-les-Nancy 54600 FR

Phone: +33 3 83 59 30 00 Email: [email protected]

Marco Davids SIDN Labs Meander 501 Arnhem 6825 MD NL


Giovane Moura SIDN Labs Meander 501 Arnhem 6825 MD NL



DOTS A. MortensenInternet-Draft Arbor NetworksIntended status: Informational F. AndreasenExpires: January 4, 2018 Cisco T. Reddy McAfee, Inc. C. Gray Comcast R. Compton Charter N. Teague Verisign July 03, 2017

Distributed-Denial-of-Service Open Threat Signaling (DOTS) Architecture draft-ietf-dots-architecture-04

Abstract

This document describes an architecture for establishing and maintaining Distributed Denial of Service (DDoS) Open Threat Signaling (DOTS) within and between domains. The document does not specify protocols or protocol extensions, instead focusing on defining architectural relationships, components and concepts used in a DOTS deployment.

Status of This Memo





Mortensen, et al. Expires January 4, 2018 [Page 1]

Internet-Draft DOTS Architecture July 2017

Copyright Notice



Table of Contents

1. Context and Motivation . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.1. Key Words . . . . . . . . . . . . . . . . . . . . . . 3 1.1.2. Definition of Terms . . . . . . . . . . . . . . . . . 3 1.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 4 2. DOTS Architecture . . . . . . . . . . . . . . . . . . . . . . 5 2.1. DOTS Operations . . . . . . . . . . . . . . . . . . . . . 8 2.2. Components . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.1. DOTS Client . . . . . . . . . . . . . . . . . . . . . 9 2.2.2. DOTS Server . . . . . . . . . . . . . . . . . . . . . 10 2.2.3. DOTS Gateway . . . . . . . . . . . . . . . . . . . . 11 2.3. DOTS Agent Relationships . . . . . . . . . . . . . . . . 12 2.3.1. Gatewayed Signaling . . . . . . . . . . . . . . . . . 14 3. Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.1. DOTS Sessions . . . . . . . . . . . . . . . . . . . . . . 16 3.1.1. Preconditions . . . . . . . . . . . . . . . . . . . . 16 3.1.2. Establishing the DOTS Session . . . . . . . . . . . . 16 3.1.3. Maintaining the DOTS Session . . . . . . . . . . . . 17 3.2. Modes of Signaling . . . . . . . . . . . . . . . . . . . 18 3.2.1. Direct Signaling . . . . . . . . . . . . . . . . . . 18 3.2.2. Redirected Signaling . . . . . . . . . . . . . . . . 18 3.2.3. Recursive Signaling . . . . . . . . . . . . . . . . . 19 3.2.4. Anycast Signaling . . . . . . . . . . . . . . . . . . 22 3.3. Triggering Requests for Mitigation . . . . . . . . . . . 23 3.3.1. Manual Mitigation Request . . . . . . . . . . . . . . 24 3.3.2. Automated Conditional Mitigation Request . . . . . . 25 3.3.3. Automated Mitigation on Loss of Signal . . . . . . . 26 4. Security Considerations . . . . . . . . . . . . . . . . . . . 26 5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 27 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27



7. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 27 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 27 8.1. Normative References . . . . . . . . . . . . . . . . . . 27 8.2. Informative References . . . . . . . . . . . . . . . . . 27 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 29

1. Context and Motivation

Signaling the need for help defending against an active distributed denial of service (DDoS) attack requires a common understanding of mechanisms and roles among the parties coordinating defensive response. The signaling layer and supplementary messaging is the focus of DDoS Open Threat Signaling (DOTS). DOTS defines a method of coordinating defensive measures among willing peers to mitigate attacks quickly and efficiently, enabling hybrid attack responses coordinated locally at or near the target of an active attack, or anywhere in-path between attack sources and target. Sample DOTS use cases are elaborated in [I-D.ietf-dots-use-cases].

This document describes an architecture used in establishing, maintaining or terminating a DOTS relationship within a domain or between domains.

1.1. Terminology

1.1.1. Key Words


1.1.2. Definition of Terms

This document uses the terms defined in [I-D.ietf-dots-requirements].

1.2. Scope

In this architecture, DOTS clients and servers communicate using DOTS signaling. As a result of signals from a DOTS client, the DOTS server may modify the forwarding path of traffic destined for the attack target(s), for example by diverting traffic to a mitigator or pool of mitigators, where policy may be applied to distinguish and discard attack traffic. Any such policy is deployment-specific.

The DOTS architecture presented here is applicable across network administrative domains - for example, between an enterprise domain and the domain of a third-party attack mitigation service - as well as to a single administrative domain. DOTS is generally assumed to



be most effective when aiding coordination of attack response between two or more participating networks, but single domain scenarios are valuable in their own right, as when aggregating intra-domain DOTS client signals for inter-domain coordinated attack response.

This document does not address any administrative or business agreements that may be established between involved DOTS parties. Those considerations are out of scope. Regardless, this document assumes necessary authentication and authorization mechanisms are put in place so that only authorized clients can invoke the DOTS service.

A detailed set of DOTS requirements are discussed in [I-D.ietf-dots-requirements], and the DOTS architecture is assumed to follow those requirements. Only new behavioral requirements are described in this document.

1.3. Assumptions

This document makes the following assumptions:

o All domains in which DOTS is deployed are assumed to offer the required connectivity between DOTS agents and any intermediary network elements, but the architecture imposes no additional limitations on the form of connectivity.

o Congestion and resource exhaustion are intended outcomes of a DDoS attack [RFC4732]. Some operators may utilize non-impacted paths or networks for DOTS, but in general conditions should be assumed to be hostile and that DOTS must be able to function in all circumstances, including when the signaling path is significantly impaired.

o There is no universal DDoS attack scale threshold triggering a coordinated response across administrative domains. A network domain administrator, or service or application owner may arbitrarily set attack scale threshold triggers, or manually send requests for mitigation.

o Mitigation requests may be sent to one or more upstream DOTS servers based on criteria determined by DOTS client administrators and the underlying network configuration. The number of DOTS servers with which a given DOTS client has established communications is determined by local policy and is deployment- specific. For example, a DOTS client of a multi-homed network may support built-in policies to establish DOTS relationships with DOTS servers located upstream of each interconnection link.



o The mitigation capacity and/or capability of domains receiving requests for coordinated attack response is opaque to the domains sending the request. The domain receiving the DOTS client signal may or may not have sufficient capacity or capability to filter any or all DDoS attack traffic directed at a target. In either case, the upstream DOTS server may redirect a request to another DOTS server. Redirection may be local to the redirecting DOTS server’s domain, or may involve a third-party domain.

o DOTS client and server signals, as well as messages sent through the data channel, are sent across any transit networks with the same probability of delivery as any other traffic between the DOTS client domain and the DOTS server domain. Any encapsulation required for successful delivery is left untouched by transit network elements. DOTS server and DOTS client cannot assume any preferential treatment of DOTS signals. Such preferential treatment may be available in some deployments (e.g., intra-domain scenarios), and the DOTS architecture does not preclude its use when available. However, DOTS itself does not address how that may be done.

o The architecture allows for, but does not assume, the presence of Quality of Service (QoS) policy agreements between DOTS-enabled peer networks or local QoS prioritization aimed at ensuring delivery of DOTS messages between DOTS agents. QoS is an operational consideration only, not a functional part of the DOTS architecture.

o The signal and data channels may be loosely coupled, and may not terminate on the same DOTS server.

2. DOTS Architecture

The basic high-level DOTS architecture is illustrated in Figure 1:





A simple example instantiation of the DOTS architecture could be an enterprise as the attack target for a volumetric DDoS attack, and an upstream DDoS mitigation service as the mitigator. The enterprise (attack target) is connected to the Internet via a link that is getting saturated, and the enterprise suspects it is under DDoS attack. The enterprise has a DOTS client, which obtains information about the DDoS attack, and signals the DOTS server for help in mitigating the attack. The DOTS server in turn invokes one or more mitigators, which are tasked with mitigating the actual DDoS attack, and hence aim to suppress the attack traffic while allowing valid traffic to reach the attack target.

The scope of the DOTS specifications is the interfaces between the DOTS client and DOTS server. The interfaces to the attack target and the mitigator are out of scope of DOTS. Similarly, the operation of both the attack target and the mitigator is out of scope of DOTS. Thus, DOTS neither specifies how an attack target decides it is under DDoS attack, nor does DOTS specify how a mitigator may actually mitigate such an attack. A DOTS client’s request for mitigation is advisory in nature, and may not lead to any mitigation at all, depending on the DOTS server domain’s capacity and willingness to mitigate on behalf of the DOTS client’s domain.

As illustrated in Figure 2, there are two interfaces between the DOTS server and the DOTS client.

+---------------+ +---------------+ | | <------- Signal Channel ------> | | | DOTS Client | | DOTS Server | | | <======= Data Channel ======> | | +---------------+ +---------------+

Figure 2: DOTS Interfaces

The DOTS client may be provided with a list of DOTS servers, each associated with one or more IP addresses. These addresses may or may not be of the same address family. The DOTS client establishes one or more sessions by connecting to the provided DOTS server addresses.

The primary purpose of the signal channel is for a DOTS client to ask a DOTS server for help in mitigating an attack, and for the DOTS server to inform the DOTS client about the status of such mitigation. The DOTS client does this by sending a client signal, which contains information about the attack target(s). The client signal may also include telemetry information about the attack, if the DOTS client has such information available. The DOTS server in turn sends a server signal to inform the DOTS client of whether it will honor the mitigation request. Assuming it will, the DOTS server initiates



attack mitigation, and periodically informs the DOTS client about the status of the mitigation. Similarly, the DOTS client periodically informs the DOTS server about the client’s status, which at a minimum provides client (attack target) health information, but it may also include telemetry information about the attack as it is now seen by the client. At some point, the DOTS client may decide to terminate the server-side attack mitigation, which it indicates to the DOTS server over the signal channel. A mitigation may also be terminated if a DOTS client-specified mitigation lifetime is exceeded. Note that the signal channel may need to operate over a link that is experiencing a DDoS attack and hence is subject to severe packet loss and high latency.

While DOTS is able to request mitigation with just the signal channel, the addition of the DOTS data channel provides for additional and more efficient capabilities; both channels are required in the DOTS architecture. The primary purpose of the data channel is to support DOTS related configuration and policy information exchange between the DOTS client and the DOTS server. Examples of such information include, but are not limited to:

o Creating identifiers, such as names or aliases, for resources for which mitigation may be requested. Such identifiers may then be used in subsequent signal channel exchanges to refer more efficiently to the resources under attack, as seen in Figure 3, using JSON to serialize the data:

{ "https1": [ "192.0.2.1:443", "198.51.100.2:443", ], "proxies": [ "203.0.113.3:3128", "[2001:db8:ac10::1]:3128" ], "api_urls": "https://apiserver.example.com/api/v1", }

Figure 3: Protected resource identifiers

o Black-list management, which enables a DOTS client to inform the DOTS server about sources to suppress.

o White-list management, which enables a DOTS client to inform the DOTS server about sources from which traffic is always accepted.



o Filter management, which enables a DOTS client to install or remove traffic filters dropping or rate-limiting unwanted traffic.

o DOTS client provisioning.

Note that while it is possible to exchange the above information before, during or after a DDoS attack, DOTS requires reliable delivery of this information and does not provide any special means for ensuring timely delivery of it during an attack. In practice, this means that DOTS deployments should not rely on such information being exchanged during a DDoS attack.

2.1. DOTS Operations

DOTS does not prescribe any specific deployment models, however DOTS is designed with some specific requirements around the different DOTS agents and their relationships.

First of all, a DOTS agent belongs to a domain that has an identity which can be authenticated and authorized. DOTS agents communicate with each other over a mutually authenticated signal channel and data channel. However, before they can do so, a service relationship needs to be established between them. The details and means by which this is done is outside the scope of DOTS, however an example would be for an enterprise A (DOTS client) to sign up for DDoS service from provider B (DOTS server). This would establish a (service) relationship between the two that enables enterprise A’s DOTS client to establish a signal channel with provider B’s DOTS server. A and B will authenticate each other, and B can verify that A is authorized for its service.

From an operational and design point of view, DOTS assumes that the above relationship is established prior to a request for DDoS attack mitigation. In particular, it is assumed that bi-directional communication is possible at this time between the DOTS client and DOTS server. Furthermore, it is assumed that additional service provisioning, configuration and information exchange can be performed by use of the data channel, if operationally required. It is not until this point that the mitigation service is available for use.

Once the mutually authenticated signal channel has been established, it will remain active. This is done to increase the likelihood that the DOTS client can signal the DOTS server for help when the attack target is being flooded, and similarly raise the probability that DOTS server signals reach the client regardless of inbound link congestion. This does not necessarily imply that the attack target and the DOTS client have to be co-located in the same administrative domain, but it is expected to be a common scenario.



DDoS mitigation with the help of an upstream mitigator may involve some form of traffic redirection whereby traffic destined for the attack target is steered towards the mitigator. Common mechanisms to achieve this redirection depend on BGP [RFC4271] and DNS [RFC1035]. The mitigator in turn inspects and scrubs the traffic, and forwards the resulting (hopefully non-attack) traffic to the attack target. Thus, when a DOTS server receives an attack mitigation request from a DOTS client, it can be viewed as a way of causing traffic redirection for the attack target indicated.

DOTS relies on mutual authentication and the pre-established service relationship between the DOTS client’s domain and the DOTS server’s domain to provide basic authorization. The DOTS server should enforce additional authorization mechanisms to restrict the mitigation scope a DOTS client can request, but such authorization mechanisms are deployment-specific.

Although co-location of DOTS server and mitigator within the same domain is expected to be a common deployment model, it is assumed that operators may require alternative models. Nothing in this document precludes such alternatives.

2.2. Components

2.2.1. DOTS Client

A DOTS client is a DOTS agent from which requests for help coordinating attack response originate. The requests may be in response to an active, ongoing attack against a target in the DOTS client’s domain, but no active attack is required for a DOTS client to request help. Operators may wish to have upstream mitigators in the network path for an indefinite period, and are restricted only by business relationships when it comes to duration and scope of requested mitigation.

The DOTS client requests attack response coordination from a DOTS server over the signal channel, including in the request the DOTS client’s desired mitigation scoping, as described in [I-D.ietf-dots-requirements]. The actual mitigation scope and countermeasures used in response to the attack are up to the DOTS server and mitigator operators, as the DOTS client may have a narrow perspective on the ongoing attack. As such, the DOTS client’s request for mitigation should be considered advisory: guarantees of DOTS server availability or mitigation capacity constitute service level agreements and are out of scope for this document.

The DOTS client adjusts mitigation scope and provides available attack details at the direction of its local administrator. Such



direction may involve manual or automated adjustments in response to feedback from the DOTS server.

To provide a metric of signal health and distinguish an idle signal channel from a disconnected or defunct session, the DOTS client sends a heartbeat over the signal channel to maintain its half of the channel. The DOTS client similarly expects a heartbeat from the DOTS server, and may consider a session terminated in the extended absence of a DOTS server heartbeat.

2.2.2. DOTS Server

A DOTS server is a DOTS agent capable of receiving, processing and possibly acting on requests for help coordinating attack response DOTS clients. The DOTS server authenticates and authorizes DOTS clients as described in Section 3.1, and maintains session state, tracking requests for mitigation, reporting on the status of active mitigations, and terminating sessions in the extended absence of a client heartbeat or when a session times out.

Assuming the preconditions discussed below exist, a DOTS client maintaining an active session with a DOTS server may reasonably expect some level of mitigation in response to a request for coordinated attack response.

The DOTS server enforces authorization of DOTS clients’ signals for mitigation. The mechanism of enforcement is not in scope for this document, but is expected to restrict requested mitigation scope to addresses, prefixes, and/or services owned by the DOTS client’s administrative domain, such that a DOTS client from one domain is not able to influence the network path to another domain. A DOTS server MUST reject requests for mitigation of resources not owned by the requesting DOTS client’s administrative domain. A DOTS server MAY also refuse a DOTS client’s mitigation request for arbitrary reasons, within any limits imposed by business or service level agreements between client and server domains. If a DOTS server refuses a DOTS client’s request for mitigation, the DOTS server SHOULD include the refusal reason in the server signal sent to the client.

A DOTS server is in regular contact with one or more mitigators. If a DOTS server accepts a DOTS client’s request for help, the DOTS server forwards a translated form of that request to the mitigator(s) responsible for scrubbing attack traffic. Note that the form of the translated request passed from the DOTS server to the mitigator is not in scope: it may be as simple as an alert to mitigator operators, or highly automated using vendor or open application programming interfaces supported by the mitigator. The DOTS server MUST report the actual scope of any mitigation enabled on behalf of a client.



The DOTS server SHOULD retrieve available metrics for any mitigations activated on behalf of a DOTS client, and SHOULD include them in server signals sent to the DOTS client originating the request for mitigation.

To provide a metric of signal health and distinguish an idle signal channel from a disconnected or defunct channel, the DOTS server MUST send a heartbeat over the signal channel to maintain its half of the channel. The DOTS server similarly expects a heartbeat from the DOTS client, and MAY consider a session terminated in the extended absence of a DOTS client heartbeat.

2.2.3. DOTS Gateway

Traditional client/server relationships may be expanded by chaining DOTS sessions. This chaining is enabled through "logical concatenation" of a DOTS server and a DOTS client, resulting in an application analogous to the SIP logical entity of a Back-to-Back User Agent (B2BUA) [RFC7092]. The term DOTS gateway is used here in the descriptions of selected scenarios involving this application.

A DOTS gateway may be deployed client-side, server-side or both. The gateway may terminate multiple discrete client connections and may aggregate these into a single or multiple DOTS sessions.

The DOTS gateway will appear as a server to its downstream agents and as a client to its upstream agents, a functional concatenation of the DOTS client and server roles, as depicted in Figure 4:

+-------------+ | | D | | +----+ | | O | | +----+ | c1 |----------| s1 | T | c2 |---------| s2 | +----+ | | S | | +----+ | | G | | +-------------+

Figure 4: DOTS gateway

The DOTS gateway MUST perform full stack DOTS session termination and reorigination between its client and server side. The details of how this is achieved are implementation specific. The DOTS protocol does not include any special features related to DOTS gateways, and hence from a DOTS perspective, whenever a DOTS gateway is present, the DOTS session simply terminates/originates there.



2.3. DOTS Agent Relationships

So far, we have only considered a relatively simple scenario of a single DOTS client associated with a single DOTS server, however DOTS supports more advanced relationships.

A DOTS server may be associated with one or more DOTS clients, and those DOTS clients may belong to different domains. An example scenario is a mitigation provider serving multiple attack targets (Figure 5).

DOTS clients DOTS server +---+ | c |----------- +---+ \ c1.example.org \ \ +---+ \ +---+ | c |----------------| S | +---+ / +---+ c1.example.com / dots1.example.net / +---+ / | c |----------- +---+ c2.example.com

Figure 5: DOTS server with multiple clients

A DOTS client may be associated with one or more DOTS servers, and those DOTS servers may belong to different domains. This may be to ensure high availability or co-ordinate mitigation with more than one directly connected ISP. An example scenario is for an enterprise to have DDoS mitigation service from multiple providers, as shown in Figure 6.



DOTS client DOTS servers +---+ -----------| S | / +---+ / dots1.example.net / +---+/ +---+ | c |---------------| S | +---+\ +---+ \ dots.example.org \ \ +---+ -----------| S | +---+ c.example.com dots2.example.net

Figure 6: Multi-Homed DOTS Client

Deploying a multi-homed client requires extra care and planning, as the DOTS servers with which the multi-homed client communicates may not be affiliated. Should the multi-homed client simultaneously request for mitigation from all servers with which it has established signal channels, the client may unintentionally inflict additional network disruption on the resources it intends to protect. In one of the worst cases, a multi-homed DOTS client could cause a permanent routing loop of traffic destined for the client’s protected protected services, as the uncoordinated DOTS servers’ mitigators all try to divert that traffic to their own scrubbing centers.

The DOTS protocol itself provides no fool-proof method to prevent such self-inflicted harms as a result deploying multi-homed DOTS clients. If DOTS client implementations nevertheless include support for multi-homing, they are expected to be aware of the risks, and consequently to include measures aimed at reducing the likelihood of negative outcomes. Simple measures might include:

o Requesting mitigation serially, ensuring only one mitigation request for a given address space is active at any given time;

o Dividing the protected resources among the DOTS servers, such that no two mitigators will be attempting to divert and scrub the same traffic;

o Restricting multi-homing to deployments in which all DOTS servers are coordinating management of a shared pool of mitigation resources.



2.3.1. Gatewayed Signaling

As discussed in Section 2.2.3, a DOTS gateway is a logical function chaining DOTS sessions through concatenation of a DOTS server and DOTS client.

An example scenario, as shown in Figure 7 and Figure 8, is for an enterprise to have deployed multiple DOTS capable devices which are able to signal intra-domain using TCP [RFC0793] on un-congested links to a DOTS gateway which may then transform these to a UDP [RFC0768] transport inter-domain where connection oriented transports may degrade; this applies to the signal channel only, as the data channel requires a connection-oriented transport. The relationship between the gateway and its upstream agents is opaque to the initial clients.

+---+ | c |\ +---+ \ +---+ \-----TCP-----| D | +---+ +---+ | O | | | | c |--------TCP-----| T |------UDP------| S | +---+ | S | | | /-----TCP-----| G | +---+ +---+ / +---+ | c |/ +---+ example.com example.com example.net DOTS clients DOTS gateway (DOTSG) DOTS server

Figure 7: Client-Side Gateway with Aggregation

+---+ | c |\ +---+ \ +---+ \-----TCP-----| D |------UDP------+---+ +---+ | O | | | | c |--------TCP-----| T |------UDP------| S | +---+ | S | | | /-----TCP-----| G |------UDP------+---+ +---+ / +---+ | c |/ +---+ example.com example.com example.net DOTS clients DOTS gateway (DOTSG) DOTS server

Figure 8: Client-Side Gateway without Aggregation



This may similarly be deployed in the inverse scenario where the gateway resides in the server-side domain and may be used to terminate and/or aggregate multiple clients to single transport as shown in figures Figure 9 and Figure 10.

+---+ | c |\ +---+ \ +---+ \-----UDP-----| D | +---+ +---+ | O | | | | c |--------TCP-----| T |------TCP------| S | +---+ | S | | | /-----TCP-----| G | +---+ +---+ / +---+ | c |/ +---+ example.com example.net example.net DOTS clients DOTS gateway (DOTSG) DOTS server

Figure 9: Server-Side Gateway with Aggregation

+---+ | c |\ +---+ \ +---+ \-----UDP-----| D |------TCP------+---+ +---+ | O | | | | c |--------TCP-----| T |------TCP------| S | +---+ | S | | | /-----UDP-----| G |------TCP------+---+ +---+ / +---+ | c |/ +---+ example.com example.net example.net DOTS clients DOTS gateway (DOTSG) DOTS server

Figure 10: Server-Side Gateway without Aggregation

This document anticipates scenarios involving multiple DOTS gateways. An example is a DOTS gateway at the network client’s side, and another one at the server side. The first gateway can be located at a CPE to aggregate requests from multiple DOTS clients enabled in an enterprise network. The second DOTS gateway is deployed on the provider side. This scenario can be seen as a combination of the client-side and server-side scenarios.



3. Concepts

3.1. DOTS Sessions

In order for DOTS to be effective as a vehicle for DDoS mitigation requests, one or more DOTS clients must establish ongoing communication with one or more DOTS servers. While the preconditions for enabling DOTS in or among network domains may also involve business relationships, service level agreements, or other formal or informal understandings between network operators, such considerations are out of scope for this document.

A DOTS session is established, bilateral exchange of data between an associated DOTS client and a DOTS server. In the DOTS architecture, data is exchanged between DOTS agents over signal and data channels. Regardless, a DOTS session is characterized by the presence of an established signal channel. A data channel associated with a signal channel may be thought of as part of the DOTS session, but the termination of that data channel does not terminate the DOTS session. Conversely, a DOTS session cannot exist without an established signal channel: when an established signal channel is terminated for any reason, the DOTS session is also said to be terminated.

3.1.1. Preconditions

Prior to establishing a DOTS session between agents, the owners of the networks, domains, services or applications involved are assumed to have agreed upon the terms of the relationship involved. Such agreements are out of scope for this document, but must be in place for a functional DOTS architecture.

It is assumed that as part of any DOTS service agreement, the DOTS client is provided with all data and metadata required to establish communication with the DOTS server. Such data and metadata would include any cryptographic information necessary to meet the message confidentiality, integrity and authenticity requirement in [I-D.ietf-dots-requirements], and might also include the pool of DOTS server addresses and ports the DOTS client should use for signal and data channel messaging.

3.1.2. Establishing the DOTS Session

With the required business agreements in place, the DOTS client initiates a signal session by contacting its DOTS server(s) over the signal channel and the data channel. To allow for DOTS service flexibility, neither the order of contact nor the time interval between channel creations is specified. A DOTS client MAY establish signal channel first, and then data channel, or vice versa.



The methods by which a DOTS client receives the address and associated service details of the DOTS server are not prescribed by this document. For example, a DOTS client may be directly configured to use a specific DOTS server IP address and port, and directly provided with any data necessary to satisfy the Peer Mutual Authentication requirement in [I-D.ietf-dots-requirements], such as symmetric or asymmetric keys, usernames and passwords, etc. All configuration and authentication information in this scenario is provided out-of-band by the domain operating the DOTS server.

At the other extreme, the architecture in this document allows for a form of DOTS client auto-provisioning. For example, the domain operating the DOTS server or servers might provide the client domain only with symmetric or asymmetric keys to authenticate the provisioned DOTS clients. Only the keys would then be directly configured on DOTS clients, but the remaining configuration required to provision the DOTS clients could be learned through mechanisms similar to DNS SRV [RFC2782] or DNS Service Discovery [RFC6763].

The DOTS client SHOULD successfully authenticate and exchange messages with the DOTS server over both signal and data channel as soon as possible to confirm that both channels are operational.

As described in [I-D.ietf-dots-requirements], the DOTS client can configure preferred values for acceptable signal loss, mitigation lifetime, and heartbeat intervals when establishing the DOTS session. A DOTS session is not active until DOTS agents have agreed on the values for these DOTS session parameters, a process defined by the protocol.

Once the DOTS client begins receiving DOTS server signals, the DOTS session is active. At any time during the DOTS session, the DOTS client may use the data channel to adjust initial configuration, manage black- and white-listed prefixes or addresses, leverage vendor-specific extensions, and so on. Note that unlike the signal channel, there is no requirement that the data channel remain operational in attack conditions (See Data Channel Requirements, [I-D.ietf-dots-requirements]).

3.1.3. Maintaining the DOTS Session

DOTS clients and servers periodically send heartbeats to each other over the signal channel, per Operational Requirements discussed in [I-D.ietf-dots-requirements]. DOTS agent operators SHOULD configure the heartbeat interval such that the frequency does not lead to accidental denials of service due to the overwhelming number of heartbeats a DOTS agent must field.



Either DOTS agent may consider a DOTS session terminated in the extended absence of a heartbeat from its peer agent. The period of that absence will be established in the protocol definition.

3.2. Modes of Signaling

This section examines the modes of signaling between agents in a DOTS architecture.

3.2.1. Direct Signaling

A DOTS session may take the form of direct signaling between the DOTS clients and servers, as shown in Figure 11.

+-------------+ +-------------+ | DOTS client |<------signal session------>| DOTS server | +-------------+ +-------------+

Figure 11: Direct Signaling

In a direct DOTS session, DOTS client and server are communicating directly. Direct signaling may exist inter- or intra-domain. The DOTS session is abstracted from the underlying networks or network elements the signals traverse: in direct signaling, the DOTS client and server are logically adjacent.

3.2.2. Redirected Signaling

In certain circumstances, a DOTS server may want to redirect a DOTS client to an alternative DOTS server for a DOTS session. Such circumstances include but are not limited to:

o Maximum number of DOTS sessions with clients has been reached;

o Mitigation capacity exhaustion in the mitigator with which the specific DOTS server is communicating;

o Mitigator outage or other downtime, such as scheduled maintenance;

o Scheduled DOTS server maintenance;

o Scheduled modifications to the network path between DOTS server and DOTS client.

A basic redirected DOTS session resembles the following, as shown in Figure 12.



+-------------+ +---------------+ | |<-(1)--- DOTS session 1 --->| | | | | | | |<=(2)== redirect to B ======| | | DOTS client | | DOTS server A | | |X-(4)--- DOTS session 1 ---X| | | | | | | | | | +-------------+ +---------------+ ^ | (3) DOTS session 2 | v +---------------+ | DOTS server B | +---------------+

Figure 12: Redirected Signaling

1. Previously established DOTS session 1 exists between a DOTS client and DOTS server A.

2. DOTS server A sends a server signal redirecting the client to DOTS server B.

3. If the DOTS client does not already have a separate DOTS session with the redirection target, the DOTS client initiates and establishes DOTS session 2 with DOTS server B.

4. Having redirected the DOTS client, DOTS server A ceases sending server signals. The DOTS client likewise stops sending client signals to DOTS server A. DOTS session 1 is terminated.

3.2.3. Recursive Signaling

DOTS is centered around improving the speed and efficiency of coordinated response to DDoS attacks. One scenario not yet discussed involves coordination among federated domains operating DOTS servers and mitigators.

In the course of normal DOTS operations, a DOTS client communicates the need for mitigation to a DOTS server, and that server initiates mitigation on a mitigator with which the server has an established service relationship. The operator of the mitigator may in turn monitor mitigation performance and capacity, as the attack being mitigated may grow in severity beyond the mitigating domain’s capabilities.



The operator of the mitigator has limited options in the event a DOTS client-requested mitigation is being overwhelmed by the severity of the attack. Out-of-scope business or service level agreements may permit the mitigating domain to drop the mitigation and let attack traffic flow unchecked to the target, but this is only encourages attack escalation. In the case where the mitigating domain is the upstream service provider for the attack target, this may mean the mitigating domain and its other services and users continue to suffer the incidental effects of the attack.

A recursive signaling model as shown in Figure 13 offers an alternative. In a variation of the use case "Enterprise with an upstream transit provider DDoS mitigation service" described in [I-D.ietf-dots-use-cases], a domain operating a DOTS server and mitigator also operates a DOTS client. This DOTS client has an established DOTS session with a DOTS server belonging to a separate administrative domain.

With these preconditions in place, the operator of the mitigator being overwhelmed or otherwise performing inadequately may request mitigation for the attack target from this separate DOTS-aware domain. Such a request recurses the originating mitigation request to the secondary DOTS server, in the hope of building a cumulative mitigation against the attack.



example.net domain . . . . . . . . . . . . . . . . . . Gn . +----+ 1 . +----+ +-----------+ . | Cc |<--------->| Sn |˜˜˜˜˜˜˜| Mitigator | . +----+ . +====+ | Mn | . . | Cn | +-----------+ . example.com . +----+ . client . ^ . . . .|. . . . . . . . . . . . . . | 1 | | . . .|. . . . . . . . . . . . . . . v . . +----+ +-----------+ . . | So |˜˜˜˜˜˜˜| Mitigator | . . +----+ | Mo | . . +-----------+ . . . . . . . . . . . . . . . . . . . . example.org domain

Figure 13: Recursive Signaling

In Figure 13, client Cc signals a request for mitigation across inter-domain DOTS session 1 to the DOTS server Sn belonging to the example.net domain. DOTS server Sn enables mitigation on mitigator Mn. DOTS server Sn is half of DOTS gateway Gn, being deployed logically back-to-back with DOTS client Cn, which has pre-existing inter-domain DOTS session 2 with the DOTS server So belonging to the example.org domain. At any point, DOTS server Sn MAY recurse an ongoing mitigation request through DOTS client Cn to DOTS server So, in the expectation that mitigator Mo will be activated to aid in the defense of the attack target.

Recursive signaling is opaque to the DOTS client. To maximize mitigation visibility to the DOTS client, however, the recursing domain SHOULD provide recursed mitigation feedback in signals reporting on mitigation status to the DOTS client. For example, the recursing domain’s mitigator should incorporate into mitigation status messages available metrics such as dropped packet or byte counts from the recursed mitigation.

DOTS clients involved in recursive signaling must be able to withdraw requests for mitigation without warning or justification, per [I-D.ietf-dots-requirements].



Operators recursing mitigation requests MAY maintain the recursed mitigation for a brief, protocol-defined period in the event the DOTS client originating the mitigation withdraws its request for help, as per the discussion of managing mitigation toggling in the operational requirements ([I-D.ietf-dots-requirements]).

Deployment of recursive signaling may result in traffic redirection, examination and mitigation extending beyond the initial bilateral relationship between DOTS client and DOTS server. As such, client control over the network path of mitigated traffic may be reduced. DOTS client operators should be aware of any privacy concerns, and work with DOTS server operators employing recursive signaling to ensure shared sensitive material is suitably protected.

3.2.4. Anycast Signaling

The DOTS architecture does not assume the availability of anycast within a DOTS deployment, but neither does the architecture exclude it. Domains operating DOTS servers MAY deploy DOTS servers with an anycast Service Address as described in BCP 126 [RFC4786]. In such a deployment, DOTS clients connecting to the DOTS Service Address may be communicating with distinct DOTS servers, depending on the network configuration at the time the DOTS clients connect. Among other benefits, anycast signaling potentially offers the following:

o Simplified DOTS client configuration, including service discovery through the methods described in [RFC7094]. In this scenario, the "instance discovery" message would be a DOTS client initiating a DOTS session to the DOTS server anycast Service Address, to which the DOTS server would reply with a redirection to the DOTS server unicast address the client should use for DOTS.

o Region- or customer-specific deployments, in which the DOTS Service Addresses route to distinct DOTS servers depending on the client region or the customer network in which a DOTS client resides.

o Operational resiliency, spreading DOTS signaling traffic across the DOTS server domain’s networks, and thereby also reducing the potential attack surface, as described in BCP 126 [RFC4786].

3.2.4.1. Anycast Signaling Considerations

As long as network configuration remains stable, anycast DOTS signaling is to the individual DOTS client indistinct from direct signaling. However, the operational challenges inherent in anycast signaling are anything but negligible, and DOTS server operators must carefully weigh the risks against the benefits before deploying.



While the DOTS signal channel primarily operates over UDP per [I-D.ietf-dots-requirements], the signal channel also requires mutual authentication between DOTS agents, with associated security state on both ends.

Network instability is of particular concern with anycast signaling, as DOTS signal channels are expected to be long-lived, and potentially operating under congested network conditions caused by a volumetric DDoS attack.

For example, a network configuration altering the route to the DOTS server during active anycast signaling may cause the DOTS client to send messages to a DOTS server other than the one with which it initially established a signaling session. That second DOTS server may not have the security state of the existing session, forcing the DOTS client to initialize a new DOTS session. This challenge might in part be mitigated by use of pre-shared keys and session resumption [RFC5246][RFC6347], but keying material must be available to all DOTS servers sharing the anycast Service Address in that case.

While the DOTS client will try to establish a new DOTS session with the DOTS server now acting as the anycast DOTS Service Address, the link between DOTS client and server may be congested with attack traffic, making signal session establishment difficult. In such a scenario, anycast Service Address instability becomes a sort of signal session flapping, with obvious negative consequences for the DOTS deployment.

Anycast signaling deployments similarly must also take into account active mitigations. Active mitigations initiated through a DOTS session may involve diverting traffic to a scrubbing center. If the DOTS session flaps due to anycast changes as described above, mitigation may also flap as the DOTS servers sharing the anycast DOTS service address toggles mitigation on detecting DOTS session loss, depending on whether the client has configured mitigation on loss of signal.

3.3. Triggering Requests for Mitigation

[I-D.ietf-dots-requirements] places no limitation on the circumstances in which a DOTS client operator may request mitigation, nor does it demand justification for any mitigation request, thereby reserving operational control over DDoS defense for the domain requesting mitigation. This architecture likewise does not prescribe the network conditions and mechanisms triggering a mitigation request from a DOTS client.



However, considering selected possible mitigation triggers from an architectural perspective offers a model for alternative or unanticipated triggers for DOTS deployments. In all cases, what network conditions merit a mitigation request are at the discretion of the DOTS client operator.

The interfaces required to trigger the mitigation request in the following scenarios are implementation-specific.

3.3.1. Manual Mitigation Request

A DOTS client operator may manually prepare a request for mitigation, including scope and duration, and manually instruct the DOTS client to send the mitigation request to the DOTS server. In context, a manual request is a request directly issued by the operator without automated decision-making performed by a device interacting with the DOTS client. Modes of manual mitigation requests include an operator entering a command into a text interface, or directly interacting with a graphical interface to send the request.

An operator might do this, for example, in response to notice of an attack delivered by attack detection equipment or software, and the alerting detector lacks interfaces or is not configured to use available interfaces to translate the alert to a mitigation request automatically.

In a variation of the above scenario, the operator may have preconfigured on the DOTS client mitigation request for various resources in the operator’s domain. When notified of an attack, the DOTS client operator manually instructs the DOTS client to send the preconfigured mitigation request for the resources under attack.

A further variant involves recursive signaling, as described in Section 3.2.3. The DOTS client in this case is the second half of a DOTS gateway (back-to-back DOTS server and client). As in the previous scenario, the scope and duration of the mitigation request are pre-existing, but in this case are derived from the mitigation request received from a downstream DOTS client by the DOTS server. Assuming the preconditions required by Section 3.2.3 are in place, the DOTS gateway operator may at any time manually request mitigation from an upstream DOTS server, sending a mitigation request derived from the downstream DOTS client’s request.

The motivations for a DOTS client operator to request mitigation manually are not prescribed by this architecture, but are expected to include some of the following:

o Notice of an attack delivered via e-mail or alternative messaging



o Notice of an attack delivered via phone call

o Notice of an attack delivered through the interface(s) of networking monitoring software deployed in the operator’s domain

o Manual monitoring of network behavior through network monitoring software

3.3.2. Automated Conditional Mitigation Request

Unlike manual mitigation requests, which depend entirely on the DOTS client operator’s capacity to react with speed and accuracy to every detected or detectable attack, mitigation requests triggered by detected attack conditions reduce the operational burden on the DOTS client operator, and minimize the latency between attack detection and the start of mitigation.

Mitigation requests are triggered in this scenario by operator- specified network conditions. Attack detection is deployment- specific, and not constrained by this architecture. Similarly the specifics of a condition are left to the discretion of the operator, though common conditions meriting mitigation include the following:

o Detected attack exceeding a rate in packets per second (pps).

o Detected attack exceeding a rate in bytes per second (bps).

o Detected resource exhaustion in an attack target.

o Detected resource exhaustion in the local domain’s mitigator.

o Number of open connections to an attack target.

o Number of attack sources in a given attack.

o Number of active attacks against targets in the operator’s domain.

o Conditional detection developed through arbitrary statistical analysis or deep learning techniques.

o Any combination of the above.

When automated conditional mitigation requests are enabled, violations of any of the above conditions, or any additional operator-defined conditions, will trigger a mitigation request from the DOTS client to the DOTS server. The interfaces between the application detecting the condition violation and the DOTS client are implementation-specific.



3.3.3. Automated Mitigation on Loss of Signal

To maintain a DOTS session, the DOTS client and the DOTS server exchange regular but infrequent messages across the signal channel. In the absence of an attack, the probability of message loss in the signaling channel should be extremely low. Under attack conditions, however, some signal loss may be anticipated as attack traffic congests the link, depending on the attack type.

While [I-D.ietf-dots-requirements] specifies the DOTS protocol be robust when signaling under attack conditions, there are nevertheless scenarios in which the DOTS signal is lost in spite of protocol best efforts. To handle such scenarios, a DOTS client operator may configure the DOTS session to trigger mitigation when the DOTS server ceases receiving DOTS client signals (or vice versa) beyond the miss count or period permitted by the protocol.

The impact of mitigating due to loss of signal in either direction must be considered carefully before enabling it. Signal loss is not caused by links congested with attack traffic alone, and as such mitigation requests triggered by signal channel degradation in either direction may incur unnecessary costs, in network performance and operational expense alike.


This section describes identified security considerations for the DOTS architecture.

DOTS is at risk from three primary attack vectors: agent impersonation, traffic injection and signal blocking. These vectors may be exploited individually or in concert by an attacker to confuse, disable, take information from, or otherwise inhibit DOTS agents.

Any attacker with the ability to impersonate a legitimate client or server or, indeed, inject false messages into the stream may potentially trigger/withdraw traffic redirection, trigger/cancel mitigation activities or subvert black/whitelists. From an architectural standpoint, operators SHOULD ensure best current practices for secure communication are observed for data and signal channel confidentiality, integrity and authenticity. Care must be taken to ensure transmission is protected by appropriately secure means, reducing attack surface by exposing only the minimal required services or interfaces. Similarly, received data at rest SHOULD be stored with a satisfactory degree of security.



As many mitigation systems employ diversion to scrub attack traffic, operators of DOTS agents SHOULD ensure DOTS sessions are resistant to Man-in-the-Middle (MitM) attacks. An attacker with control of a DOTS client may negatively influence network traffic by requesting and withdrawing requests for mitigation for particular prefixes, leading to route or DNS flapping.

Any attack targeting the availability of DOTS servers may disrupt the ability of the system to receive and process DOTS signals resulting in failure to fulfill a mitigation request. DOTS agents SHOULD be given adequate protections, again in accordance with best current practices for network and host security.

5. Contributors

Mohamed Boucadair Orange

[email protected]

6. Acknowledgments

Thanks to Matt Richardson and Med Boucadair for their comments and suggestions.

7. Change Log

2016-03-18 Initial revision

8. References




[I-D.ietf-dots-requirements] Mortensen, A., Moskowitz, R., and T. Reddy, "Distributed Denial of Service (DDoS) Open Threat Signaling Requirements", draft-ietf-dots-requirements-05 (work in progress), June 2017.




[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI 10.17487/RFC0768, August 1980, <http://www.rfc-editor.org/info/rfc768>.

[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, DOI 10.17487/RFC0793, September 1981, <http://www.rfc-editor.org/info/rfc793>.

[RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, <http://www.rfc-editor.org/info/rfc1035>.

[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, DOI 10.17487/RFC2782, February 2000, <http://www.rfc-editor.org/info/rfc2782>.

[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006, <http://www.rfc-editor.org/info/rfc4271>.


[RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786, December 2006, <http://www.rfc-editor.org/info/rfc4786>.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, <http://www.rfc-editor.org/info/rfc5246>.




[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, <http://www.rfc-editor.org/info/rfc6763>.

[RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session Initiation Protocol (SIP) Back-to-Back User Agents", RFC 7092, DOI 10.17487/RFC7092, December 2013, <http://www.rfc-editor.org/info/rfc7092>.

[RFC7094] McPherson, D., Oran, D., Thaler, D., and E. Osterweil, "Architectural Considerations of IP Anycast", RFC 7094, DOI 10.17487/RFC7094, January 2014, <http://www.rfc-editor.org/info/rfc7094>.


Andrew Mortensen Arbor Networks 2727 S. State St Ann Arbor, MI 48104 United States

EMail: [email protected]

Flemming Andreasen Cisco United States




Christopher Gray Comcast United States




Rich Compton Charter


Nik Teague Verisign United States



DOTS A. Mortensen, Ed.Internet-Draft ForcepointIntended status: Informational T. Reddy, Ed.Expires: September 7, 2020 McAfee, Inc. F. Andreasen Cisco N. Teague Iron Mountain R. Compton Charter March 6, 2020

Distributed-Denial-of-Service Open Threat Signaling (DOTS) Architecture draft-ietf-dots-architecture-18

Abstract

This document describes an architecture for establishing and maintaining Distributed Denial of Service (DDoS) Open Threat Signaling (DOTS) within and between domains. The document does not specify protocols or protocol extensions, instead focusing on defining architectural relationships, components and concepts used in a DOTS deployment.

Status of This Memo




This Internet-Draft will expire on September 7, 2020.

Copyright Notice


Mortensen, et al. Expires September 7, 2020 [Page 1]

Internet-Draft DOTS Architecture March 2020


Table of Contents

1. Context and Motivation . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.1. Key Words . . . . . . . . . . . . . . . . . . . . . . 3 1.1.2. Definition of Terms . . . . . . . . . . . . . . . . . 3 1.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 4 2. DOTS Architecture . . . . . . . . . . . . . . . . . . . . . . 5 2.1. DOTS Operations . . . . . . . . . . . . . . . . . . . . . 8 2.2. Components . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.1. DOTS Client . . . . . . . . . . . . . . . . . . . . . 9 2.2.2. DOTS Server . . . . . . . . . . . . . . . . . . . . . 10 2.2.3. DOTS Gateway . . . . . . . . . . . . . . . . . . . . 11 2.3. DOTS Agent Relationships . . . . . . . . . . . . . . . . 12 2.3.1. Gatewayed Signaling . . . . . . . . . . . . . . . . . 14 3. Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.1. DOTS Sessions . . . . . . . . . . . . . . . . . . . . . . 16 3.1.1. Preconditions . . . . . . . . . . . . . . . . . . . . 17 3.1.2. Establishing the DOTS Session . . . . . . . . . . . . 17 3.1.3. Maintaining the DOTS Session . . . . . . . . . . . . 18 3.2. Modes of Signaling . . . . . . . . . . . . . . . . . . . 18 3.2.1. Direct Signaling . . . . . . . . . . . . . . . . . . 19 3.2.2. Redirected Signaling . . . . . . . . . . . . . . . . 19 3.2.3. Recursive Signaling . . . . . . . . . . . . . . . . . 20 3.2.4. Anycast Signaling . . . . . . . . . . . . . . . . . . 23 3.2.5. Signaling Considerations for Network Address Translation . . . . . . . . . . . . . . . . . . . . . 25 3.3. Triggering Requests for Mitigation . . . . . . . . . . . 27 3.3.1. Manual Mitigation Request . . . . . . . . . . . . . . 28 3.3.2. Automated Conditional Mitigation Request . . . . . . 29 3.3.3. Automated Mitigation on Loss of Signal . . . . . . . 30 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 5. Security Considerations . . . . . . . . . . . . . . . . . . . 30 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 31 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 31 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 32 8.1. Normative References . . . . . . . . . . . . . . . . . . 32



8.2. Informative References . . . . . . . . . . . . . . . . . 32 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 35

1. Context and Motivation

Signaling the need for help to defend against an active distributed denial of service (DDoS) attack requires a common understanding of mechanisms and roles among the parties coordinating defensive response. The signaling layer and supplementary messaging is the focus of DDoS Open Threat Signaling (DOTS). DOTS defines a method of coordinating defensive measures among willing peers to mitigate attacks quickly and efficiently, enabling hybrid attack responses coordinated locally at or near the target of an active attack, or anywhere in-path between attack sources and target. Sample DOTS use cases are elaborated in [I-D.ietf-dots-use-cases].

This document describes an architecture used in establishing, maintaining or terminating a DOTS relationship within a domain or between domains.

1.1. Terminology

1.1.1. Key Words

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

1.1.2. Definition of Terms

This document uses the terms defined in [RFC8612].

1.2. Scope

In this architecture, DOTS clients and servers communicate using DOTS signal channel [I-D.ietf-dots-signal-channel] and data channel [I-D.ietf-dots-data-channel] protocols.

The DOTS architecture presented here is applicable across network administrative domains - for example, between an enterprise domain and the domain of a third-party attack mitigation service - as well as to a single administrative domain. DOTS is generally assumed to be most effective when aiding coordination of attack response between two or more participating networks, but single domain scenarios are valuable in their own right, as when aggregating intra-domain DOTS client signals for inter-domain coordinated attack response.



This document does not address any administrative or business agreements that may be established between involved DOTS parties. Those considerations are out of scope. Regardless, this document assumes necessary authentication and authorization mechanisms are put in place so that only authorized clients can invoke the DOTS service.

A detailed set of DOTS requirements are discussed in [RFC8612], and the DOTS architecture is designed to follow those requirements. Only new behavioral requirements are described in this document.

1.3. Assumptions

This document makes the following assumptions:

o All domains in which DOTS is deployed are assumed to offer the required connectivity between DOTS agents and any intermediary network elements, but the architecture imposes no additional limitations on the form of connectivity.

o Congestion and resource exhaustion are intended outcomes of a DDoS attack [RFC4732]. Some operators may utilize non-impacted paths or networks for DOTS, but in general conditions should be assumed to be hostile and DOTS must be able to function in all circumstances, including when the signaling path is significantly impaired. Congestion control requirements are discussed in Section 3 of [RFC8612]. DOTS signal channel defined in [I-D.ietf-dots-signal-channel] is designed to be extremely resilient under extremely hostile network conditions and provides continued contact between DOTS agents even as DDoS attack traffic saturates the link.

o There is no universal DDoS attack scale threshold triggering a coordinated response across administrative domains. A network domain administrator, or service or application owner may arbitrarily set attack scale threshold triggers, or manually send requests for mitigation.

o Mitigation requests may be sent to one or more upstream DOTS servers based on criteria determined by DOTS client administrators and the underlying network configuration. The number of DOTS servers with which a given DOTS client has established communications is determined by local policy and is deployment- specific. For example, a DOTS client of a multi-homed network may support built-in policies to establish DOTS relationships with DOTS servers located upstream of each interconnection link.

o The mitigation capacity and/or capability of domains receiving requests for coordinated attack response is opaque to the domains



sending the request. The domain receiving the DOTS client signal may or may not have sufficient capacity or capability to filter any or all DDoS attack traffic directed at a target. In either case, the upstream DOTS server may redirect a request to another DOTS server. Redirection may be local to the redirecting DOTS server’s domain, or may involve a third-party domain.

o DOTS client and server signals, as well as messages sent through the data channel, are sent across any transit networks with the same probability of delivery as any other traffic between the DOTS client domain and the DOTS server domain. Any encapsulation required for successful delivery is left untouched by transit network elements. DOTS server and DOTS client cannot assume any preferential treatment of DOTS signals. Such preferential treatment may be available in some deployments (e.g., intra-domain scenarios), and the DOTS architecture does not preclude its use when available. However, DOTS itself does not address how that may be done.

o The architecture allows for, but does not assume, the presence of Quality of Service (QoS) policy agreements between DOTS-enabled peer networks or local QoS prioritization aimed at ensuring delivery of DOTS messages between DOTS agents. QoS is an operational consideration only, not a functional part of the DOTS architecture.

o The signal and data channels are loosely coupled, and might not terminate on the same DOTS server. How the DOTS servers synchronize the DOTS configuration is out of scope of this specification.

2. DOTS Architecture

The basic high-level DOTS architecture is illustrated in Figure 1:





A simple example instantiation of the DOTS architecture could be an enterprise as the attack target for a volumetric DDoS attack, and an upstream DDoS mitigation service as the mitigator. The service provided by the mitigator is called: DDoS mitigation service. The enterprise (attack target) is connected to the Internet via a link that is getting saturated, and the enterprise suspects it is under DDoS attack. The enterprise has a DOTS client, which obtains information about the DDoS attack, and signals the DOTS server for help in mitigating the attack. The DOTS server in turn invokes one or more mitigators, which are tasked with mitigating the actual DDoS attack, and hence aim to suppress the attack traffic while allowing valid traffic to reach the attack target.

The scope of the DOTS specifications is the interfaces between the DOTS client and DOTS server. The interfaces to the attack target and the mitigator are out of scope of DOTS. Similarly, the operation of both the attack target and the mitigator is out of scope of DOTS. Thus, DOTS specifies neither how an attack target decides it is under DDoS attack, nor does DOTS specify how a mitigator may actually mitigate such an attack. A DOTS client’s request for mitigation is advisory in nature, and might not lead to any mitigation at all, depending on the DOTS server domain’s capacity and willingness to mitigate on behalf of the DOTS client domain.

The DOTS client may be provided with a list of DOTS servers, each associated with one or more IP addresses. These addresses may or may not be of the same address family. The DOTS client establishes one or more sessions by connecting to the provided DOTS server addresses.

As illustrated in Figure 2, there are two interfaces between a DOTS server and a DOTS client; a signal channel and (optionally) a data channel.


Figure 2: DOTS Interfaces

The primary purpose of the signal channel is for a DOTS client to ask a DOTS server for help in mitigating an attack, and for the DOTS server to inform the DOTS client about the status of such mitigation. The DOTS client does this by sending a client signal, which contains information about the attack target(s). The client signal may also include telemetry information about the attack, if the DOTS client has such information available. The DOTS server in turn sends a



server signal to inform the DOTS client of whether it will honor the mitigation request. Assuming it will, the DOTS server initiates attack mitigation, and periodically informs the DOTS client about the status of the mitigation. Similarly, the DOTS client periodically informs the DOTS server about the client’s status, which at a minimum provides client (attack target) health information, but it should also include efficacy information about the attack mitigation as it is now seen by the client. At some point, the DOTS client may decide to terminate the server-side attack mitigation, which it indicates to the DOTS server over the signal channel. A mitigation may also be terminated if a DOTS client-specified mitigation lifetime is exceeded. Note that the signal channel may need to operate over a link that is experiencing a DDoS attack and hence is subject to severe packet loss and high latency.

While DOTS is able to request mitigation with just the signal channel, the addition of the DOTS data channel provides for additional and more efficient capabilities. The primary purpose of the data channel is to support DOTS related configuration and policy information exchange between the DOTS client and the DOTS server. Examples of such information include, but are not limited to:

o Creating identifiers, such as names or aliases, for resources for which mitigation may be requested. Such identifiers may then be used in subsequent signal channel exchanges to refer more efficiently to the resources under attack.

o Drop-list management, which enables a DOTS client to inform the DOTS server about sources to suppress.

o Accept-list management, which enables a DOTS client to inform the DOTS server about sources from which traffic is always accepted.

o Filter management, which enables a DOTS client to install or remove traffic filters dropping or rate-limiting unwanted traffic.

o DOTS client provisioning.

Note that while it is possible to exchange the above information before, during or after a DDoS attack, DOTS requires reliable delivery of this information and does not provide any special means for ensuring timely delivery of it during an attack. In practice, this means that DOTS deployments should rely on such information being exchanged only under normal traffic conditions.



2.1. DOTS Operations

DOTS does not prescribe any specific deployment models, however DOTS is designed with some specific requirements around the different DOTS agents and their relationships.

First of all, a DOTS agent belongs to a domain that has an identity which can be authenticated and authorized. DOTS agents communicate with each other over a mutually authenticated signal channel and (optionally) data channel. However, before they can do so, a service relationship needs to be established between them. The details and means by which this is done is outside the scope of DOTS, however an example would be for an enterprise A (DOTS client) to sign up for DDoS service from provider B (DOTS server). This would establish a (service) relationship between the two that enables enterprise A’s DOTS client to establish a signal channel with provider B’s DOTS server. A and B will authenticate each other, and B can verify that A is authorized for its service.

From an operational and design point of view, DOTS assumes that the above relationship is established prior to a request for DDoS attack mitigation. In particular, it is assumed that bi-directional communication is possible at this time between the DOTS client and DOTS server. Furthermore, it is assumed that additional service provisioning, configuration and information exchange can be performed by use of the data channel, if operationally required. It is not until this point that the mitigation service is available for use.

Once the mutually authenticated signal channel has been established, it will remain active. This is done to increase the likelihood that the DOTS client can signal the DOTS server for help when the attack target is being flooded, and similarly raise the probability that DOTS server signals reach the client regardless of inbound link congestion. This does not necessarily imply that the attack target and the DOTS client have to be co-located in the same administrative domain, but it is expected to be a common scenario.

DDoS mitigation with the help of an upstream mitigator may involve some form of traffic redirection whereby traffic destined for the attack target is steered towards the mitigator. Common mechanisms to achieve this redirection depend on BGP [RFC4271] and DNS [RFC1035]. The mitigator in turn inspects and scrubs the traffic, and forwards the resulting (hopefully non-attack) traffic to the attack target. Thus, when a DOTS server receives an attack mitigation request from a DOTS client, it can be viewed as a way of causing traffic redirection for the attack target indicated.



DOTS relies on mutual authentication and the pre-established service relationship between the DOTS client domain and the DOTS server domain to provide authorization. The DOTS server should enforce authorization mechanisms to restrict the mitigation scope a DOTS client can request, but such authorization mechanisms are deployment- specific.

Although co-location of DOTS server and mitigator within the same domain is expected to be a common deployment model, it is assumed that operators may require alternative models. Nothing in this document precludes such alternatives.

2.2. Components

2.2.1. DOTS Client

A DOTS client is a DOTS agent from which requests for help coordinating attack response originate. The requests may be in response to an active, ongoing attack against a target in the DOTS client domain, but no active attack is required for a DOTS client to request help. Operators may wish to have upstream mitigators in the network path for an indefinite period, and are restricted only by business relationships when it comes to duration and scope of requested mitigation.

The DOTS client requests attack response coordination from a DOTS server over the signal channel, including in the request the DOTS client’s desired mitigation scoping, as described in [RFC8612] (SIG- 008). The actual mitigation scope and countermeasures used in response to the attack are up to the DOTS server and mitigator operators, as the DOTS client may have a narrow perspective on the ongoing attack. As such, the DOTS client’s request for mitigation should be considered advisory: guarantees of DOTS server availability or mitigation capacity constitute service level agreements and are out of scope for this document.

The DOTS client adjusts mitigation scope and provides available mitigation feedback (e.g., mitigation efficacy) at the direction of its local administrator. Such direction may involve manual or automated adjustments in response to updates from the DOTS server.

To provide a metric of signal health and distinguish an idle signal channel from a disconnected or defunct session, the DOTS client sends a heartbeat over the signal channel to maintain its half of the channel. The DOTS client similarly expects a heartbeat from the DOTS server, and may consider a session terminated in the extended absence of a DOTS server heartbeat.



2.2.2. DOTS Server

A DOTS server is a DOTS agent capable of receiving, processing and possibly acting on requests for help coordinating attack response from DOTS clients. The DOTS server authenticates and authorizes DOTS clients as described in Section 3.1, and maintains session state, tracking requests for mitigation, reporting on the status of active mitigations, and terminating sessions in the extended absence of a client heartbeat or when a session times out.

Assuming the preconditions discussed below exist, a DOTS client maintaining an active session with a DOTS server may reasonably expect some level of mitigation in response to a request for coordinated attack response.

For a given DOTS client (administrative) domain, the DOTS server needs to be able to determine whether a given resource is in that domain. For example, this could take the form of associating a set of IP addresses and/or prefixes per DOTS client domain. The DOTS server enforces authorization of signals for mitigation, filtering rules and aliases for resources from DOTS clients. The mechanism of enforcement is not in scope for this document, but is expected to restrict mitigation requests, filtering rules and aliases scope to addresses, prefixes, and/or services owned by the DOTS client domain, such that a DOTS client from one domain is not able to influence the network path to another domain. A DOTS server MUST reject mitigation requests, filtering rules and aliases for resources not owned by the requesting DOTS client’s administrative domain. The exact mechanism for the DOTS servers to validate that the resources are within the scope of the DOTS client domain is deployment-specific. For example, if the DOTS client domain uses Provider-Aggregatable prefixes for its resources and leverages the DDoS mitigation service of the Internet Transit Provider (ITP), the ITP knows the prefixes assigned to the DOTS client domain because they are assigned by the ITP itself. However, if the DDoS Mitigation is offered by a third party DDoS mitigation service provider, it does not know the resources owned by the DOTS client domain. The DDoS mitigation service provider and the DOTS client domain can opt to use the identifier validation challenges discussed in [RFC8555] and [I-D.ietf-acme-ip] to identify whether the DOTS client domain actually controls the resources. The challenges for validating control of resources must be performed when no attack traffic is present and works only for "dns" and "ip" identifier types. Further, if the DOTS client lies about the resources owned by the DOTS client domain, the DDoS mitigation service provider can impose penalties for violating the service level agreement. A DOTS server MAY also refuse a DOTS client’s mitigation request for arbitrary reasons, within any limits imposed by business or service level agreements between client and server domains. If a



DOTS server refuses a DOTS client’s request for mitigation, the DOTS server MUST include the refusal reason in the server signal sent to the client.

A DOTS server is in regular contact with one or more mitigators. If a DOTS server accepts a DOTS client’s request for help, the DOTS server forwards a translated form of that request to the mitigator(s) responsible for scrubbing attack traffic. Note that the form of the translated request passed from the DOTS server to the mitigator is not in scope: it may be as simple as an alert to mitigator operators, or highly automated using vendor or open application programming interfaces supported by the mitigator. The DOTS server MUST report the actual scope of any mitigation enabled on behalf of a client.

The DOTS server SHOULD retrieve available metrics for any mitigations activated on behalf of a DOTS client, and SHOULD include them in server signals sent to the DOTS client originating the request for mitigation.

To provide a metric of signal health and distinguish an idle signal channel from a disconnected or defunct channel, the DOTS server MUST send a heartbeat over the signal channel to maintain its half of the channel. The DOTS server similarly expects a heartbeat from the DOTS client, and MAY consider a session terminated in the extended absence of a DOTS client heartbeat.

2.2.3. DOTS Gateway

Traditional client/server relationships may be expanded by chaining DOTS sessions. This chaining is enabled through "logical concatenation" of a DOTS server and a DOTS client, resulting in an application analogous to the Session Initiation Protocol (SIP) [RFC3261] logical entity of a Back-to-Back User Agent (B2BUA) [RFC7092]. The term DOTS gateway is used here in the descriptions of selected scenarios involving this application.

A DOTS gateway may be deployed client-side, server-side or both. The gateway may terminate multiple discrete client connections and may aggregate these into a single or multiple DOTS sessions.

The DOTS gateway will appear as a server to its downstream agents and as a client to its upstream agents, a functional concatenation of the DOTS client and server roles, as depicted in Figure 3:



+-------------+ | | D | | +----+ | | O | | +----+ | c1 |----------| s1 | T | c2 |---------| s2 | +----+ | | S | | +----+ | | G | | +-------------+

Figure 3: DOTS gateway

The DOTS gateway MUST perform full stack DOTS session termination and reorigination between its client and server side. The details of how this is achieved are implementation specific.

2.3. DOTS Agent Relationships

So far, we have only considered a relatively simple scenario of a single DOTS client associated with a single DOTS server, however DOTS supports more advanced relationships.

A DOTS server may be associated with one or more DOTS clients, and those DOTS clients may belong to different domains. An example scenario is a mitigation provider serving multiple attack targets (Figure 4).

DOTS clients DOTS server +---+ | c |----------- +---+ \ c1.example.org \ \ +---+ \ +---+ | c |----------------| S | +---+ / +---+ c1.example.com / dots1.example.net / +---+ / | c |----------- +---+ c2.example.com

Figure 4: DOTS server with multiple clients

A DOTS client may be associated with one or more DOTS servers, and those DOTS servers may belong to different domains. This may be to ensure high availability or co-ordinate mitigation with more than one directly connected ISP. An example scenario is for an enterprise to



have DDoS mitigation service from multiple providers, as shown in Figure 5.

DOTS client DOTS servers +---+ -----------| S | / +---+ / dots1.example.net / +---+/ +---+ | c |---------------| S | +---+\ +---+ \ dots.example.org \ \ +---+ -----------| S | +---+ c.example.com dots2.example.net

Figure 5: Multi-Homed DOTS Client

Deploying a multi-homed client requires extra care and planning, as the DOTS servers with which the multi-homed client communicates might not be affiliated. Should the multi-homed client simultaneously request for mitigation from all servers with which it has established signal channels, the client may unintentionally inflict additional network disruption on the resources it intends to protect. In one of the worst cases, a multi-homed DOTS client could cause a permanent routing loop of traffic destined for the client’s protected services, as the uncoordinated DOTS servers’ mitigators all try to divert that traffic to their own scrubbing centers.

The DOTS protocol itself provides no fool-proof method to prevent such self-inflicted harms as a result deploying multi-homed DOTS clients. If DOTS client implementations nevertheless include support for multi-homing, they are expected to be aware of the risks, and consequently to include measures aimed at reducing the likelihood of negative outcomes. Simple measures might include:

o Requesting mitigation serially, ensuring only one mitigation request for a given address space is active at any given time;

o Dividing the protected resources among the DOTS servers, such that no two mitigators will be attempting to divert and scrub the same traffic;



o Restricting multi-homing to deployments in which all DOTS servers are coordinating management of a shared pool of mitigation resources.

2.3.1. Gatewayed Signaling

As discussed in Section 2.2.3, a DOTS gateway is a logical function chaining DOTS sessions through concatenation of a DOTS server and DOTS client.

An example scenario, as shown in Figure 6 and Figure 7, is for an enterprise to have deployed multiple DOTS capable devices which are able to signal intra-domain using TCP [RFC0793] on un-congested links to a DOTS gateway which may then transform these to a UDP [RFC0768] transport inter-domain where connection oriented transports may degrade; this applies to the signal channel only, as the data channel requires a connection-oriented transport. The relationship between the gateway and its upstream agents is opaque to the initial clients.

+---+ | c |\ +---+ \ +---+ \-----TCP-----| D | +---+ +---+ | O | | | | c |--------TCP-----| T |------UDP------| S | +---+ | S | | | /-----TCP-----| G | +---+ +---+ / +---+ | c |/ +---+ example.com example.com example.net DOTS clients DOTS gateway (DOTSG) DOTS server

Figure 6: Client-Side Gateway with Aggregation



+---+ | c |\ +---+ \ +---+ \-----TCP-----| D |------UDP------+---+ +---+ | O | | | | c |--------TCP-----| T |------UDP------| S | +---+ | S | | | /-----TCP-----| G |------UDP------+---+ +---+ / +---+ | c |/ +---+ example.com example.com example.net DOTS clients DOTS gateway (DOTSG) DOTS server

Figure 7: Client-Side Gateway without Aggregation

This may similarly be deployed in the inverse scenario where the gateway resides in the server-side domain and may be used to terminate and/or aggregate multiple clients to single transport as shown in figures Figure 8 and Figure 9.

+---+ | c |\ +---+ \ +---+ \-----UDP-----| D | +---+ +---+ | O | | | | c |--------TCP-----| T |------TCP------| S | +---+ | S | | | /-----TCP-----| G | +---+ +---+ / +---+ | c |/ +---+ example.com example.net example.net DOTS clients DOTS gateway (DOTSG) DOTS server

Figure 8: Server-Side Gateway with Aggregation



+---+ | c |\ +---+ \ +---+ \-----UDP-----| D |------TCP------+---+ +---+ | O | | | | c |--------TCP-----| T |------TCP------| S | +---+ | S | | | /-----UDP-----| G |------TCP------+---+ +---+ / +---+ | c |/ +---+ example.com example.net example.net DOTS clients DOTS gateway (DOTSG) DOTS server

Figure 9: Server-Side Gateway without Aggregation

This document anticipates scenarios involving multiple DOTS gateways. An example is a DOTS gateway at the network client’s side, and another one at the server side. The first gateway can be located at a Customer Premises Equipment (CPE) to aggregate requests from multiple DOTS clients enabled in an enterprise network. The second DOTS gateway is deployed on the provider side. This scenario can be seen as a combination of the client-side and server-side scenarios.

3. Concepts

3.1. DOTS Sessions

In order for DOTS to be effective as a vehicle for DDoS mitigation requests, one or more DOTS clients must establish ongoing communication with one or more DOTS servers. While the preconditions for enabling DOTS in or among network domains may also involve business relationships, service level agreements, or other formal or informal understandings between network operators, such considerations are out of scope for this document.

A DOTS session is established to support bilateral exchange of data between an associated DOTS client and a DOTS server. In the DOTS architecture, data is exchanged between DOTS agents over signal and data channels. As such, a DOTS session can be a DOTS signal channel session, a DOTS data channel session, or both. The DOTS server couples the DOTS signal and data channel sessions using the DOTS client identity. The DOTS session is further elaborated in the DOTS signal channel protocol defined in [I-D.ietf-dots-signal-channel] and the DOTS data channel protocol defined in [I-D.ietf-dots-data-channel].

A DOTS agent can maintain one or more DOTS sessions.



A DOTS signal channel session is associated with a single transport connection (TCP or UDP session) and an security association (a TLS or DTLS session). Similarly, a DOTS data channel session is associated with a single TCP connection and an TLS security association.

Mitigation requests created using DOTS signal channel are not bound to the DOTS signal channel session. Instead, mitigation requests are associated with a DOTS client and can be managed using different DOTS signal channel sessions.

3.1.1. Preconditions

Prior to establishing a DOTS session between agents, the owners of the networks, domains, services or applications involved are assumed to have agreed upon the terms of the relationship involved. Such agreements are out of scope for this document, but must be in place for a functional DOTS architecture.

It is assumed that as part of any DOTS service agreement, the DOTS client is provided with all data and metadata required to establish communication with the DOTS server. Such data and metadata would include any cryptographic information necessary to meet the message confidentiality, integrity and authenticity requirement (SEC-002) in [RFC8612], and might also include the pool of DOTS server addresses and ports the DOTS client should use for signal and data channel messaging.

3.1.2. Establishing the DOTS Session

With the required business agreements in place, the DOTS client initiates a DOTS session by contacting its DOTS server(s) over the signal channel and (possibly) the data channel. To allow for DOTS service flexibility, neither the order of contact nor the time interval between channel creations is specified. A DOTS client MAY establish signal channel first, and then data channel, or vice versa.

The methods by which a DOTS client receives the address and associated service details of the DOTS server are not prescribed by this document. For example, a DOTS client may be directly configured to use a specific DOTS server IP address and port, and directly provided with any data necessary to satisfy the Peer Mutual Authentication requirement (SEC-001) in [RFC8612], such as symmetric or asymmetric keys, usernames and passwords, etc. All configuration and authentication information in this scenario is provided out-of- band by the domain operating the DOTS server.

At the other extreme, the architecture in this document allows for a form of DOTS client auto-provisioning. For example, the domain



operating the DOTS server or servers might provide the client domain only with symmetric or asymmetric keys to authenticate the provisioned DOTS clients. Only the keys would then be directly configured on DOTS clients, but the remaining configuration required to provision the DOTS clients could be learned through mechanisms similar to DNS SRV [RFC2782] or DNS Service Discovery [RFC6763].

The DOTS client SHOULD successfully authenticate and exchange messages with the DOTS server over both signal and (if used) data channel as soon as possible to confirm that both channels are operational.

As described in [RFC8612] (DM-008), the DOTS client can configure preferred values for acceptable signal loss, mitigation lifetime, and heartbeat intervals when establishing the DOTS signal channel session. A DOTS signal channel session is not active until DOTS agents have agreed on the values for these DOTS session parameters, a process defined by the protocol.

Once the DOTS client begins receiving DOTS server signals, the DOTS session is active. At any time during the DOTS session, the DOTS client may use the data channel to manage aliases, manage drop- and accept-listed prefixes or addresses, leverage vendor-specific extensions, and so on. Note that unlike the signal channel, there is no requirement that the data channel remains operational in attack conditions (See Data Channel Requirements, Section 2.3 of [RFC8612]).

3.1.3. Maintaining the DOTS Session

DOTS clients and servers periodically send heartbeats to each other over the signal channel, discussed in [RFC8612] (SIG-004). DOTS agent operators SHOULD configure the heartbeat interval such that the frequency does not lead to accidental denials of service due to the overwhelming number of heartbeats a DOTS agent must field.

Either DOTS agent may consider a DOTS signal channel session terminated in the extended absence of a heartbeat from its peer agent. The period of that absence will be established in the protocol definition.

3.2. Modes of Signaling

This section examines the modes of signaling between agents in a DOTS architecture.



3.2.1. Direct Signaling

A DOTS session may take the form of direct signaling between the DOTS clients and servers, as shown in Figure 10.

+-------------+ +-------------+ | DOTS client |<------signal session------>| DOTS server | +-------------+ +-------------+

Figure 10: Direct Signaling

In a direct DOTS session, the DOTS client and server are communicating directly. Direct signaling may exist inter- or intra- domain. The DOTS session is abstracted from the underlying networks or network elements the signals traverse: in direct signaling, the DOTS client and server are logically adjacent.

3.2.2. Redirected Signaling

In certain circumstances, a DOTS server may want to redirect a DOTS client to an alternative DOTS server for a DOTS signal channel session. Such circumstances include but are not limited to:

o Maximum number of DOTS signal channel sessions with clients has been reached;

o Mitigation capacity exhaustion in the mitigator with which the specific DOTS server is communicating;

o Mitigator outage or other downtime, such as scheduled maintenance;

o Scheduled DOTS server maintenance;

o Scheduled modifications to the network path between DOTS server and DOTS client.

A basic redirected DOTS signal channel session resembles the following, as shown in Figure 11.



+-------------+ +---------------+ | |<-(1)--- DOTS signal ------>| | | | channel session 1 | | | |<=(2)== redirect to B ======| | | DOTS client | | DOTS server A | | |X-(4)--- DOTS signal ------X| | | | channel session 1 | | | | | | +-------------+ +---------------+ ^ | (3) DOTS signal channel | session 2 v +---------------+ | DOTS server B | +---------------+

Figure 11: Redirected Signaling

1. Previously established DOTS signal channel session 1 exists between a DOTS client and DOTS server A.

2. DOTS server A sends a server signal redirecting the client to DOTS server B.

3. If the DOTS client does not already have a separate DOTS signal channel session with the redirection target, the DOTS client initiates and establishes DOTS signal channel session 2 with DOTS server B.

4. Having redirected the DOTS client, DOTS server A ceases sending server signals. The DOTS client likewise stops sending client signals to DOTS server A. DOTS signal channel session 1 is terminated.

3.2.3. Recursive Signaling

DOTS is centered around improving the speed and efficiency of coordinated response to DDoS attacks. One scenario not yet discussed involves coordination among federated domains operating DOTS servers and mitigators.

In the course of normal DOTS operations, a DOTS client communicates the need for mitigation to a DOTS server, and that server initiates mitigation on a mitigator with which the server has an established service relationship. The operator of the mitigator may in turn monitor mitigation performance and capacity, as the attack being



mitigated may grow in severity beyond the mitigating domain’s capabilities.

The operator of the mitigator has limited options in the event a DOTS client-requested mitigation is being overwhelmed by the severity of the attack. Out-of-scope business or service level agreements may permit the mitigating domain to drop the mitigation and let attack traffic flow unchecked to the target, but this only encourages attack escalation. In the case where the mitigating domain is the upstream service provider for the attack target, this may mean the mitigating domain and its other services and users continue to suffer the incidental effects of the attack.

A recursive signaling model as shown in Figure 12 offers an alternative. In a variation of the use case "Upstream DDoS Mitigation by an Upstream Internet Transit Provider" described in [I-D.ietf-dots-use-cases], a domain operating a DOTS server and mitigator also operates a DOTS client. This DOTS client has an established DOTS session with a DOTS server belonging to a separate administrative domain.

With these preconditions in place, the operator of the mitigator being overwhelmed or otherwise performing inadequately may request mitigation for the attack target from this separate DOTS-aware domain. Such a request recurses the originating mitigation request to the secondary DOTS server, in the hope of building a cumulative mitigation against the attack.



example.net domain . . . . . . . . . . . . . . . . . . Gn . +----+ 1 . +----+ +-----------+ . | Cc |<--------->| Sn |˜˜˜˜˜˜˜| Mitigator | . +----+ . +====+ | Mn | . . | Cn | +-----------+ . example.com . +----+ . client . ^ . . . .|. . . . . . . . . . . . . . | 2 | | . . .|. . . . . . . . . . . . . . . v . . +----+ +-----------+ . . | So |˜˜˜˜˜˜˜| Mitigator | . . +----+ | Mo | . . +-----------+ . . . . . . . . . . . . . . . . . . . . example.org domain

Figure 12: Recursive Signaling

In Figure 12, client Cc signals a request for mitigation across inter-domain DOTS session 1 to the DOTS server Sn belonging to the example.net domain. DOTS server Sn enables mitigation on mitigator Mn. DOTS server Sn is half of DOTS gateway Gn, being deployed logically back-to-back with DOTS client Cn, which has pre-existing inter-domain DOTS session 2 with the DOTS server So belonging to the example.org domain. At any point, DOTS server Sn MAY recurse an ongoing mitigation request through DOTS client Cn to DOTS server So, in the expectation that mitigator Mo will be activated to aid in the defense of the attack target.

Recursive signaling is opaque to the DOTS client. To maximize mitigation visibility to the DOTS client, however, the recursing domain SHOULD provide recursed mitigation feedback in signals reporting on mitigation status to the DOTS client. For example, the recursing domain’s DOTS server should incorporate into mitigation status messages available metrics such as dropped packet or byte counts from the recursed domain’s DOTS server.

DOTS clients involved in recursive signaling must be able to withdraw requests for mitigation without warning or justification, per SIG-006 in [RFC8612].



Operators recursing mitigation requests MAY maintain the recursed mitigation for a brief, protocol-defined period in the event the DOTS client originating the mitigation withdraws its request for help, as per the discussion of managing mitigation toggling in SIG-006 of [RFC8612].

Deployment of recursive signaling may result in traffic redirection, examination and mitigation extending beyond the initial bilateral relationship between DOTS client and DOTS server. As such, client control over the network path of mitigated traffic may be reduced. DOTS client operators should be aware of any privacy concerns, and work with DOTS server operators employing recursive signaling to ensure shared sensitive material is suitably protected. Typically there is a contractual Service Level Agreement (SLA) negotiated among the DOTS client domain, the recursed domain and the recursing domain to meet the privacy requirements of the DOTS client domain and authorization for the recursing domain to request mitigation for the resources controlled by the DOTS client domain.

3.2.4. Anycast Signaling

The DOTS architecture does not assume the availability of anycast within a DOTS deployment, but neither does the architecture exclude it. Domains operating DOTS servers MAY deploy DOTS servers with an anycast Service Address as described in BCP 126 [RFC4786]. In such a deployment, DOTS clients connecting to the DOTS Service Address may be communicating with distinct DOTS servers, depending on the network configuration at the time the DOTS clients connect. Among other benefits, anycast signaling potentially offers the following:

o Simplified DOTS client configuration, including service discovery through the methods described in [RFC7094]. In this scenario, the "instance discovery" message would be a DOTS client initiating a DOTS session to the DOTS server anycast Service Address, to which the DOTS server would reply with a redirection to the DOTS server unicast address the client should use for DOTS.

o Region- or customer-specific deployments, in which the DOTS Service Addresses route to distinct DOTS servers depending on the client region or the customer network in which a DOTS client resides.

o Operational resiliency, spreading DOTS signaling traffic across the DOTS server domain’s networks, and thereby also reducing the potential attack surface, as described in BCP 126 [RFC4786].



3.2.4.1. Anycast Signaling Considerations

As long as network configuration remains stable, anycast DOTS signaling is to the individual DOTS client indistinct from direct signaling. However, the operational challenges inherent in anycast signaling are anything but negligible, and DOTS server operators must carefully weigh the risks against the benefits before deploying.

While the DOTS signal channel primarily operates over UDP per SIG-001 in [RFC8612], the signal channel also requires mutual authentication between DOTS agents, with associated security state on both ends.

Network instability is of particular concern with anycast signaling, as DOTS signal channels are expected to be long-lived, and potentially operating under congested network conditions caused by a volumetric DDoS attack.

For example, a network configuration altering the route to the DOTS server during active anycast signaling may cause the DOTS client to send messages to a DOTS server other than the one with which it initially established a signaling session. That second DOTS server might not have the security state of the existing session, forcing the DOTS client to initialize a new DOTS session. This challenge might in part be mitigated by use of resumption via a PSK in TLS 1.3 [RFC8446] and DTLS 1.3 [I-D.ietf-tls-dtls13] (session resumption in TLS 1.2 [RFC5246] and DTLS 1.2 [RFC6347]), but keying material must be available to all DOTS servers sharing the anycast Service Address in that case which has operational challenges of its own.

While the DOTS client will try to establish a new DOTS session with the DOTS server now acting as the anycast DOTS Service Address, the link between DOTS client and server may be congested with attack traffic, making signal session establishment difficult. In such a scenario, anycast Service Address instability becomes a sort of signal session flapping, with obvious negative consequences for the DOTS deployment.

Anycast signaling deployments similarly must also take into account active mitigations. Active mitigations initiated through a DOTS session may involve diverting traffic to a scrubbing center. If the DOTS session flaps due to anycast changes as described above, mitigation may also flap as the DOTS servers sharing the anycast DOTS service address toggles mitigation on detecting DOTS session loss, depending on whether the client has configured mitigation on loss of signal (Section 3.3.3).



3.2.5. Signaling Considerations for Network Address Translation

Network address translators (NATs) are expected to be a common feature of DOTS deployments. The Middlebox Traversal Guidelines in [RFC8085] include general NAT considerations that are applicable to DOTS deployments when the signal channel is established over UDP.

Additional DOTS-specific considerations arise when NATs are part of the DOTS architecture. For example, DDoS attack detection behind a NAT will detect attacks against internal addresses. A DOTS client subsequently asked to request mitigation for the attacked scope of addresses cannot reasonably perform the task, due to the lack of externally routable addresses in the mitigation scope.

The following considerations do not cover all possible scenarios, but are meant rather to highlight anticipated common issues when signaling through NATs.

3.2.5.1. Direct Provisioning of Internal-to-External Address Mappings

Operators may circumvent the problem of translating internal addresses or prefixes to externally routable mitigation scopes by directly provisioning the mappings of external addresses to internal protected resources on the DOTS client. When the operator requests mitigation scoped for internal addresses, directly or through automated means, the DOTS client looks up the matching external addresses or prefixes, and issues a mitigation request scoped to that externally routable information.

When directly provisioning the address mappings, operators must ensure the mappings remain up to date, or risk losing the ability to request accurate mitigation scopes. To that aim, the DOTS client can rely on mechanisms such as [RFC8512] or [RFC7658] to retrieve static explicit mappings. This document does not prescribe the method by which mappings are maintained once they are provisioned on the DOTS client.

3.2.5.2. Resolving Public Mitigation Scope with Port Control Protocol (PCP)

Port Control Protocol (PCP) [RFC6887] may be used to retrieve the external addresses/prefixes and/or port numbers if the NAT function embeds a PCP server.

A DOTS client can use the information retrieved by means of PCP to feed the DOTS protocol(s) messages that will be sent to a DOTS server. These messages will convey the external addresses/prefixes as set by the NAT.



PCP also enables discovery and configuration of the lifetime of port mappings instantiated in intermediate NAT devices. Discovery of port mapping lifetimes can reduce the dependency on heartbeat messages to maintain mappings, and therefore reduce the load on DOTS servers and the network.

3.2.5.3. Resolving Public Mitigation Scope with Session Traversal Utilities (STUN)

An internal resource, e.g., a Web server, can discover its reflexive transport address through a STUN Binding request/response transaction, as described in [I-D.ietf-tram-stunbis]. After learning its reflexive transport address from the STUN server, the internal resource can export its reflexive transport address and internal transport address to the DOTS client, thereby enabling the DOTS client to request mitigation with the correct external scope, as depicted in Figure 13. The mechanism for providing the DOTS client with the reflexive transport address and internal transport address is unspecified in this document.

In order to prevent an attacker from modifying the STUN messages in transit, the STUN client and server must use the message-integrity mechanism discussed in Section 9 of [I-D.ietf-tram-stunbis] or use STUN over DTLS [RFC7350] or use STUN over TLS. If the STUN client is behind a NAT that performs Endpoint-Dependent Mapping [RFC5128], the internal service cannot provide the DOTS client with the reflexive transport address discovered using STUN. The behavior of a NAT between the STUN client and the STUN server could be discovered using the experimental techniques discussed in [RFC5780], but note that there is currently no standardized way for a STUN client to reliably determine if it is behind a NAT that performs Endpoint-Dependent Mapping.



Binding Binding +--------+ request +---+ request +--------+ | STUN |<----------| N |<----------| STUN | | server | | A | | client | | |---------->| T |---------->| | +--------+ Binding +---+ Binding +--------+ response response | | reflexive transport address | & internal transport address v +--------+ | DOTS | | client | +--------+

Figure 13: Resolving mitigation scope with STUN

3.2.5.4. Resolving Requested Mitigation Scope with DNS

DOTS supports mitigation scoped to DNS names. As discussed in [RFC3235], using DNS names instead of IP addresses potentially avoids the address translation problem, as long as the same domain name is internally and externally resolvable. For example, a detected attack’s internal target address can be mapped to a DNS name through a reverse lookup. The DNS name returned by the reverse lookup can then be provided to the DOTS client as the external scope for mitigation. For the reverse DNS lookup, DNS Security Extensions (DNSSEC) [RFC4033] must be used where the authenticity of response is critical.

3.3. Triggering Requests for Mitigation

[RFC8612] places no limitation on the circumstances in which a DOTS client operator may request mitigation, nor does it demand justification for any mitigation request, thereby reserving operational control over DDoS defense for the domain requesting mitigation. This architecture likewise does not prescribe the network conditions and mechanisms triggering a mitigation request from a DOTS client.

However, considering selected possible mitigation triggers from an architectural perspective offers a model for alternative or unanticipated triggers for DOTS deployments. In all cases, what network conditions merit a mitigation request are at the discretion of the DOTS client operator.



The mitigation request itself is defined by DOTS, however the interfaces required to trigger the mitigation request in the following scenarios are implementation-specific.

3.3.1. Manual Mitigation Request

A DOTS client operator may manually prepare a request for mitigation, including scope and duration, and manually instruct the DOTS client to send the mitigation request to the DOTS server. In context, a manual request is a request directly issued by the operator without automated decision-making performed by a device interacting with the DOTS client. Modes of manual mitigation requests include an operator entering a command into a text interface, or directly interacting with a graphical interface to send the request.

An operator might do this, for example, in response to notice of an attack delivered by attack detection equipment or software, and the alerting detector lacks interfaces or is not configured to use available interfaces to translate the alert to a mitigation request automatically.

In a variation of the above scenario, the operator may have preconfigured on the DOTS client mitigation requests for various resources in the operator’s domain. When notified of an attack, the DOTS client operator manually instructs the DOTS client to send the relevant preconfigured mitigation request for the resources under attack.

A further variant involves recursive signaling, as described in Section 3.2.3. The DOTS client in this case is the second half of a DOTS gateway (back-to-back DOTS server and client). As in the previous scenario, the scope and duration of the mitigation request are pre-existing, but in this case are derived from the mitigation request received from a downstream DOTS client by the DOTS server. Assuming the preconditions required by Section 3.2.3 are in place, the DOTS gateway operator may at any time manually request mitigation from an upstream DOTS server, sending a mitigation request derived from the downstream DOTS client’s request.

The motivations for a DOTS client operator to request mitigation manually are not prescribed by this architecture, but are expected to include some of the following:

o Notice of an attack delivered via e-mail or alternative messaging

o Notice of an attack delivered via phone call



o Notice of an attack delivered through the interface(s) of networking monitoring software deployed in the operator’s domain

o Manual monitoring of network behavior through network monitoring software

3.3.2. Automated Conditional Mitigation Request

Unlike manual mitigation requests, which depend entirely on the DOTS client operator’s capacity to react with speed and accuracy to every detected or detectable attack, mitigation requests triggered by detected attack conditions reduce the operational burden on the DOTS client operator, and minimize the latency between attack detection and the start of mitigation.

Mitigation requests are triggered in this scenario by operator- specified network conditions. Attack detection is deployment- specific, and not constrained by this architecture. Similarly the specifics of a condition are left to the discretion of the operator, though common conditions meriting mitigation include the following:

o Detected attack exceeding a rate in packets per second (pps).

o Detected attack exceeding a rate in bytes per second (bps).

o Detected resource exhaustion in an attack target.

o Detected resource exhaustion in the local domain’s mitigator.

o Number of open connections to an attack target.

o Number of attack sources in a given attack.

o Number of active attacks against targets in the operator’s domain.

o Conditional detection developed through arbitrary statistical analysis or deep learning techniques.

o Any combination of the above.

When automated conditional mitigation requests are enabled, violations of any of the above conditions, or any additional operator-defined conditions, will trigger a mitigation request from the DOTS client to the DOTS server. The interfaces between the application detecting the condition violation and the DOTS client are implementation-specific.



3.3.3. Automated Mitigation on Loss of Signal

To maintain a DOTS signal channel session, the DOTS client and the DOTS server exchange regular but infrequent messages across the signal channel. In the absence of an attack, the probability of message loss in the signaling channel should be extremely low. Under attack conditions, however, some signal loss may be anticipated as attack traffic congests the link, depending on the attack type.

While [RFC8612] specifies the DOTS protocol be robust when signaling under attack conditions, there are nevertheless scenarios in which the DOTS signal is lost in spite of protocol best efforts. To handle such scenarios, a DOTS operator may request one or more mitigations which are triggered only when the DOTS server ceases receiving DOTS client heartbeats beyond the miss count or interval permitted by the protocol.

The impact of mitigating due to loss of signal in either direction must be considered carefully before enabling it. Attack traffic congesting links is not the only reason why signal could be lost, and as such mitigation requests triggered by signal channel degradation in either direction may incur unnecessary costs due to scrubbing traffic, adversely impact network performance and operational expense alike.


This document has no actions for IANA.


This section describes identified security considerations for the DOTS architecture.

Security considerations and security requirements discussed in [RFC8612] need to be taken into account.

DOTS is at risk from three primary attack vectors: agent impersonation, traffic injection and signal blocking. These vectors may be exploited individually or in concert by an attacker to confuse, disable, take information from, or otherwise inhibit DOTS agents.

Any attacker with the ability to impersonate a legitimate DOTS client or server or, indeed, inject false messages into the stream may potentially trigger/withdraw traffic redirection, trigger/cancel mitigation activities or subvert drop-/accept-lists. From an architectural standpoint, operators MUST ensure conformance to the



security requirements defined in Section 2.4 of [RFC8612] to secure data in transit. Similarly, as the received data may contain network topology, telemetry, threat and mitigation information which could be considered sensitive in certain environment, it SHOULD be protected at rest per required local policy.

DOTS agents MUST perform mutual authentication to ensure authenticity of each other and DOTS servers MUST verify that the requesting DOTS client is authorized to request mitigation for specific target resources (see Section 2.2.2).

An MITM attacker can intercept and drop packets, preventing the DOTS peers from receiving some or all of the DOTS messages, automated mitigation on loss of signal can be used as a countermeasure but with risks discussed in Section 3.3.3.

An attacker with control of a DOTS client may negatively influence network traffic by requesting and withdrawing requests for mitigation for particular prefixes, leading to route or DNS flapping. DOTS operators should carefully monitor and audit DOTS clients to detect misbehavior and deter misuse.

Any attack targeting the availability of DOTS servers may disrupt the ability of the system to receive and process DOTS signals resulting in failure to fulfill a mitigation request. DOTS servers MUST be given adequate protections, in accordance with best current practices for network and host security.

6. Contributors


[email protected]

Christopher Gray [email protected]

7. Acknowledgments

Thanks to Matt Richardson, Roman Danyliw, Frank Xialiang, Roland Dobbins, Wei Pan, Kaname Nishizuka, Jon Shallow, Paul Kyzivat, Warren Kumari, Benjamin Kaduk, and Mohamed Boucadair for their comments and suggestions.

Special thanks to Roman Danyliw for the AD review.



8. References



[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, DOI 10.17487/RFC4033, March 2005, <https://www.rfc-editor.org/info/rfc4033>.

[RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786, December 2006, <https://www.rfc-editor.org/info/rfc4786>.

[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and P. Selkirk, "Port Control Protocol (PCP)", RFC 6887, DOI 10.17487/RFC6887, April 2013, <https://www.rfc-editor.org/info/rfc6887>.


[RFC8612] Mortensen, A., Reddy, T., and R. Moskowitz, "DDoS Open Threat Signaling (DOTS) Requirements", RFC 8612, DOI 10.17487/RFC8612, May 2019, <https://www.rfc-editor.org/info/rfc8612>.


[I-D.ietf-acme-ip] Shoemaker, R., "ACME IP Identifier Validation Extension", draft-ietf-acme-ip-08 (work in progress), October 2019.

[I-D.ietf-dots-data-channel] Boucadair, M. and T. Reddy.K, "Distributed Denial-of- Service Open Threat Signaling (DOTS) Data Channel Specification", draft-ietf-dots-data-channel-31 (work in progress), July 2019.



[I-D.ietf-dots-signal-channel] Reddy.K, T., Boucadair, M., Patil, P., Mortensen, A., and N. Teague, "Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification", draft- ietf-dots-signal-channel-41 (work in progress), January 2020.

[I-D.ietf-dots-use-cases] Dobbins, R., Migault, D., Moskowitz, R., Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS Open Threat Signaling", draft-ietf-dots-use-cases-20 (work in progress), September 2019.

[I-D.ietf-tls-dtls13] Rescorla, E., Tschofenig, H., and N. Modadugu, "The Datagram Transport Layer Security (DTLS) Protocol Version 1.3", draft-ietf-tls-dtls13-34 (work in progress), November 2019.

[I-D.ietf-tram-stunbis] Petit-Huguenin, M., Salgueiro, G., Rosenberg, J., Wing, D., Mahy, R., and P. Matthews, "Session Traversal Utilities for NAT (STUN)", draft-ietf-tram-stunbis-21 (work in progress), March 2019.

[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI 10.17487/RFC0768, August 1980, <https://www.rfc-editor.org/info/rfc768>.

[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, DOI 10.17487/RFC0793, September 1981, <https://www.rfc-editor.org/info/rfc793>.

[RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, <https://www.rfc-editor.org/info/rfc1035>.

[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, DOI 10.17487/RFC2782, February 2000, <https://www.rfc-editor.org/info/rfc2782>.

[RFC3235] Senie, D., "Network Address Translator (NAT)-Friendly Application Design Guidelines", RFC 3235, DOI 10.17487/RFC3235, January 2002, <https://www.rfc-editor.org/info/rfc3235>.



[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, DOI 10.17487/RFC3261, June 2002, <https://www.rfc-editor.org/info/rfc3261>.

[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006, <https://www.rfc-editor.org/info/rfc4271>.


[RFC5128] Srisuresh, P., Ford, B., and D. Kegel, "State of Peer-to- Peer (P2P) Communication across Network Address Translators (NATs)", RFC 5128, DOI 10.17487/RFC5128, March 2008, <https://www.rfc-editor.org/info/rfc5128>.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, <https://www.rfc-editor.org/info/rfc5246>.

[RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery Using Session Traversal Utilities for NAT (STUN)", RFC 5780, DOI 10.17487/RFC5780, May 2010, <https://www.rfc-editor.org/info/rfc5780>.

[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012, <https://www.rfc-editor.org/info/rfc6347>.

[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, <https://www.rfc-editor.org/info/rfc6763>.

[RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session Initiation Protocol (SIP) Back-to-Back User Agents", RFC 7092, DOI 10.17487/RFC7092, December 2013, <https://www.rfc-editor.org/info/rfc7092>.

[RFC7094] McPherson, D., Oran, D., Thaler, D., and E. Osterweil, "Architectural Considerations of IP Anycast", RFC 7094, DOI 10.17487/RFC7094, January 2014, <https://www.rfc-editor.org/info/rfc7094>.



[RFC7350] Petit-Huguenin, M. and G. Salgueiro, "Datagram Transport Layer Security (DTLS) as Transport for Session Traversal Utilities for NAT (STUN)", RFC 7350, DOI 10.17487/RFC7350, August 2014, <https://www.rfc-editor.org/info/rfc7350>.

[RFC7658] Perreault, S., Tsou, T., Sivakumar, S., and T. Taylor, "Deprecation of MIB Module NAT-MIB: Managed Objects for Network Address Translators (NATs)", RFC 7658, DOI 10.17487/RFC7658, October 2015, <https://www.rfc-editor.org/info/rfc7658>.

[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, March 2017, <https://www.rfc-editor.org/info/rfc8085>.

[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, <https://www.rfc-editor.org/info/rfc8446>.

[RFC8512] Boucadair, M., Ed., Sivakumar, S., Jacquenet, C., Vinapamula, S., and Q. Wu, "A YANG Module for Network Address Translation (NAT) and Network Prefix Translation (NPT)", RFC 8512, DOI 10.17487/RFC8512, January 2019, <https://www.rfc-editor.org/info/rfc8512>.

[RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J. Kasten, "Automatic Certificate Management Environment (ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019, <https://www.rfc-editor.org/info/rfc8555>.


Andrew Mortensen (editor) Forcepoint United States


Tirumaleswar Reddy (editor) McAfee, Inc. Embassy Golf Link Business Park Bangalore, Karnataka 560071 India




Flemming Andreasen Cisco United States


Nik Teague Iron Mountain United States


Rich Compton Charter



DOTS T. ReddyInternet-Draft McAfeeIntended status: Standards Track M. BoucadairExpires: December 24, 2017 Orange K. Nishizuka NTT Communications L. Xia Huawei P. Patil Cisco A. Mortensen Arbor Networks, Inc. N. Teague Verisign, Inc. June 22, 2017

Distributed Denial-of-Service Open Threat Signaling (DOTS) Data Channel draft-ietf-dots-data-channel-02

Abstract

The document specifies a Distributed Denial-of-Service Open Threat Signaling (DOTS) data channel used for bulk exchange of data not easily or appropriately communicated through the DOTS signal channel under attack conditions. This is a companion document to the DOTS signal channel specification.

Status of This Memo




This Internet-Draft will expire on December 24, 2017.

Reddy, et al. Expires December 24, 2017 [Page 1]

Internet-Draft DOTS Data Channel June 2017

Copyright Notice



Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions and Terminology . . . . . . . . . . . 4 3. DOTS Data Channel . . . . . . . . . . . . . . . . . . . . . . 4 3.1. DOTS Data Channel YANG Model . . . . . . . . . . . . . . 6 3.1.1. Identifier Model structure . . . . . . . . . . . . . 6 3.1.2. Identifier Model . . . . . . . . . . . . . . . . . . 6 3.1.3. Filter Model structure . . . . . . . . . . . . . . . 8 3.1.4. Filter Model . . . . . . . . . . . . . . . . . . . . 9 3.2. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 11 3.2.1. Create Identifiers . . . . . . . . . . . . . . . . . 11 3.2.2. Delete Identifiers . . . . . . . . . . . . . . . . . 13 3.2.3. Retrieving Installed Identifiers . . . . . . . . . . 14 3.3. Filtering Rules . . . . . . . . . . . . . . . . . . . . . 16 3.3.1. Install Filtering Rules . . . . . . . . . . . . . . . 16 3.3.2. Remove Filtering Rules . . . . . . . . . . . . . . . 18 3.3.3. Retrieving Installed Filtering Rules . . . . . . . . 18 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 4.1. DOTS Data Channel JSON Attribute Mappings Registry . . . 19 4.2. Registration Template . . . . . . . . . . . . . . . . . . 19 4.3. Initial Registry Contents . . . . . . . . . . . . . . . . 19 5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 21 6. Security Considerations . . . . . . . . . . . . . . . . . . . 21 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 8.1. Normative References . . . . . . . . . . . . . . . . . . 22 8.2. Informative References . . . . . . . . . . . . . . . . . 23 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 24



1. Introduction

A distributed denial-of-service (DDoS) attack is an attempt to make machines or network resources unavailable to their intended users. In most cases, sufficient scale can be achieved by compromising enough end-hosts and using those infected hosts to perpetrate and amplify the attack. The victim in this attack can be an application server, a client, a router, a firewall, or an entire network.

DDoS Open Threat Signaling (DOTS) defines two channels: signal and data channels [I-D.ietf-dots-architecture] (Figure 1). The DOTS signal channel used to convey that a network is under a DDOS attack to an upstream DOTS server so that appropriate mitigation actions are undertaken on the suspect traffic is further elaborated in [I-D.ietf-dots-signal-channel]. The DOTS data channel is used for infrequent bulk data exchange between DOTS agents in the aim to significantly augment attack response coordination.


Figure 1: DOTS Channels

Section 2 of [I-D.ietf-dots-architecture] identifies that the DOTS data channel is used to perform the tasks listed below:

o Filter management, which enables a DOTS client to request the installation or removal of traffic filters, dropping or rate- limiting unwanted traffic and permitting white-listed traffic. Sample use cases for populating black- or white-list filtering rules are detailed hereafter:

A. If a network resource (DOTS client) detects a potential DDoS attack from a set of IP addresses, the DOTS client informs its servicing router (DOTS gateway) of all suspect IP addresses that need to be blocked or black-listed for further investigation. The DOTS client could also specify a list of protocols and ports in the black-list rule. That DOTS gateway in-turn propagates the black-listed IP addresses to the DOTS server which will undertake appropriate action so that traffic from these IP addresses to the target network (specified by the DOTS client) is blocked.

B. A network has partner sites from which only legitimate traffic arrives and the network wants to ensure that the traffic from



these sites is not penalized during DDOS attacks. The DOTS client uses the DOTS data channel to convey the white-listed IP addresses or prefixes of the partner sites to its DOTS server. The DOTS server uses this information to white-list flows from such IP addresses or prefixes reaching the network.

o Creating identifiers, such as names or aliases, for resources for which mitigation may be requested:

A. The DOTS client may submit to the DOTS server a collection of prefixes which it would like to refer to by alias when requesting mitigation. The server can respond to this request with either with a success or failure response (see requirement OP-006 in [I-D.ietf-dots-requirements] and Section 2 in [I-D.ietf-dots-architecture]).

2. Notational Conventions and Terminology


The reader should be familiar with the terms defined in [I-D.ietf-dots-architecture].

For simplicity, all of the examples in this document use "/restconf" as the discovered RESTCONF API root path. Many protocol header lines and message-body text within examples throughout the document are split into multiple lines for display purposes only. When a line ends with backslash (’\’) as the last character, the line is wrapped for display purposes. It is to be considered to be joined to the next line by deleting the backslash, the following line break, and the leading whitespace of the next line.

3. DOTS Data Channel

The DOTS data channel is intended to be used for bulk data exchanges between DOTS agents. Unlike the signal channel, which must operate nominally even when confronted with signal degradation due to packet loss, the data channel is not expected to be constructed to deal with DDoS attack conditions.

As the primary function of the data channel is data exchange, a reliable transport is required in order for DOTS agents to detect data delivery success or failure. RESTCONF [RFC8040] over TLS [RFC5246] over TCP is used for DOTS data channel (Figure 2). RESTCONF uses HTTP methods to provide CRUD operations on a conceptual datastore containing YANG-defined data, which is compatible with a



server which implements NETCONF datastores. The HTTP POST, PUT, PATCH, and DELETE methods are used to edit data resources represented by DOTS data channel YANG data models. These basic edit operations allow the DOTS data channel running configuration to be altered by a DOTS client. DOTS data channel configuration data and state data can be retrieved with the GET method. HTTP status codes are used to report success or failure for RESTCONF operations. The DOTS client will perform the root resource discovery procedure discussed in Section 3.1 of [RFC8040] to determine the root of the RESTCONF API. After discovering the RESTCONF API root, the DOTS client MUST use this value as the initial part of the path in the request URI, in any subsequent request to the DOTS server. The DOTS server can optionally support retrieval of the YANG modules it supports (Section 3.7 in [RFC8040]), for example, DOTS client can use RESTCONF to retrieve the company proprietary YANG model supported by the DOTS server.

Note: This document uses RESTCONF, a protocol based on HTTP [RFC7230], for configuring data defined in YANG version 1 [RFC6020] or YANG version 1.1 [RFC7950], using the datastore concepts defined in the Network Configuration Protocol (NETCONF) [RFC6241]. RESTCONF combines the simplicity of the HTTP protocol with the predictability and automation potential of a schema-driven API. RESTCONF offers a simple subset of NETCONF functionality and provides a simplified interface using REST-like API which addresses the needs of the DOTS data channel and hence an optimal choice.

+--------------+ | DOTS | +--------------+ | RESTCONF | +--------------+ | TLS | +--------------+ | TCP | +--------------+ | IP | +--------------+

Figure 2: Abstract Layering of DOTS data channel over RESTCONF over TLS

JavaScript Object Notation (JSON) [RFC7159] payload is used to propagate data channel specific payload messages that convey request parameters and response information such as errors. This specification uses the encoding rules defined in [RFC7951] for representing DOTS data channel configuration data defined using YANG (Section 3.1) as JSON text.



A DOTS client registers itself to its DOTS server(s) in order to set up DOTS data channel related configuration data on the DOTS server and receive state data (i.e., non-configuration data) from the DOTS server. A single DOTS data channel between DOTS agents can be used to exchange multiple requests and multiple responses. To reduce DOTS client and DOTS server workload, DOTS client SHOULD re-use the TLS session. While the communication to the DOTS server is quiescent, the DOTS client MAY probe the server to ensure it has maintained cryptographic state. Such probes can also keep alive firewall or NAT bindings. A TLS heartbeat [RFC6520] verifies the DOTS server still has TLS state by returning a TLS message.

3.1. DOTS Data Channel YANG Model

3.1.1. Identifier Model structure

This document defines a YANG [RFC6020] data model for creating identifiers, such as names or aliases, for resources for which mitigation may be requested. Such identifiers may then be used in subsequent DOTS signal channel exchanges to refer more efficiently to the resources under attack.

This document defines the YANG module "ietf-dots-data-channel- identifier", which has the following structure:

module: ietf-dots-data-channel-identifier +--rw identifier +--rw alias* [alias-name] +--rw alias-name string +--rw ip* inet:ip-address +--rw prefix* inet:ip-prefix +--rw port-range* [lower-port upper-port] | +--rw lower-port inet:port-number | +--rw upper-port inet:port-number +--rw traffic-protocol* uint8 +--rw fqdn* inet:domain-name +--rw uri* inet:uri

3.1.2. Identifier Model

<CODE BEGINS> file "[email protected]"

module ietf-dots-data-channel-identifier { namespace "urn:ietf:params:xml:ns:yang:ietf-dots-data-channel-identifier"; prefix "alias"; import ietf-inet-types { prefix "inet"; }



organization "McAfee, Inc."; contact "Konda, Tirumaleswar Reddy <[email protected]>";

description "This module contains YANG definition for configuring identifiers for resources using DOTS data channel";

revision 2016-11-28 { reference "https://tools.ietf.org/html/draft-reddy-dots-data-channel"; }

container identifier { description "top level container for identifiers"; list alias { key alias-name; description "list of identifiers"; leaf alias-name { type string; description "alias name"; } leaf-list ip { type inet:ip-address; description "IP address"; } leaf-list prefix { type inet:ip-prefix; description "prefix"; } list port-range { key "lower-port upper-port"; description "Port range. When only lower-port is present, it represents a single port."; leaf lower-port { type inet:port-number; mandatory true; description "lower port"; } leaf upper-port { type inet:port-number; must ". >= ../lower-port" { error-message "The upper-port must be greater than or equal to lower-port"; } description "upper port"; }



} leaf-list traffic-protocol { type uint8; description "Internet Protocol number"; } leaf-list fqdn { type inet:domain-name; description "FQDN"; } leaf-list uri { type inet:uri; description "URI"; } } } } <CODE ENDS>

3.1.3. Filter Model structure

This document extends the "ietf-access-control-list" Access Control List (ACL) YANG data model [I-D.ietf-netmod-acl-model] for the configuration of filtering rules. ACL is explained in Section 1 of [I-D.ietf-netmod-acl-model].

Examples of such configuration include:

o Black-list management, which enables a DOTS client to inform the DOTS server about sources from which traffic should be suppressed.

o White-list management, which enables a DOTS client to inform the DOTS server about sources from which traffic should always be accepted.

o Filter management, which enables a DOTS client to request the installation or removal of traffic filters, dropping or rate- limiting unwanted traffic and permitting white-listed traffic.

This document defines the YANG module "ietf-dots-access-control-list" to extend the "ietf-access-control-list" module to handle fragmented packets and to support rate-limit action. Filtering fragments adds an additional layer of protection against a denial-of-service (DoS) attack that uses only noninitial fragments. When there is only Layer 3 information in the ACL entry and the fragments keyword is present, for noninitial fragments matching the ACL entry, the deny or permit action associated with the ACL entry will be enforced and for initial or non-fragment matching the ACL entry, the the next ACL entry will be processed. When there is both Layer 3 and Layer 4 information in



the ACL entry and the fragments keyword is present, the ACL action is conservative for both permit and deny actions. The actions are conservative to not accidentally deny a fragmented portion of a flow because the fragments do not contain sufficient information to match all of the filter attributes. In the deny action case, instead of denying a non-initial fragment, the next ACL entry is processed. In the permit case, it is assumed that the Layer 4 information in the packet, if available, matches the Layer 4 information in the ACL entry.

The "ietf-dots-access-control-list" module has the following structure:

module: ietf-dots-access-control-list augment /ietf-acl:access-lists/ietf-acl:acl/ietf-acl:access-list-entries/ietf-acl:ace/ietf-acl:actions/ietf-acl:packet-handling: +--:(rate-limit) +--rw rate-limit? decimal64 augment /ietf-acl:access-lists/ietf-acl:acl/ietf-acl:access-list-entries/ietf-acl:ace: +--rw fragments? empty

3.1.4. Filter Model

This YANG module augments the "ietf-access-control-list" YANG data model defined in [I-D.ietf-netmod-acl-model].




module ietf-dots-access-control-list { namespace "urn:ietf:params:xml:ns:yang:ietf-dots-access-control-list"; prefix "dots-acl"; import ietf-access-control-list { prefix "ietf-acl"; } organization "McAfee, Inc."; contact "Konda, Tirumaleswar Reddy <[email protected]>";

description "This module contains YANG definition for configuring filtering rules using DOTS data channel";

revision 2017-06-12 { reference "https://tools.ietf.org/html/draft-ietf-dots-data-channel"; }

augment "/ietf-acl:access-lists/ietf-acl:acl/ietf-acl:access-list-entries/ietf-acl:ace/ietf-acl:actions/ietf-acl:packet-handling" {

description "rate-limit action";

case rate-limit { leaf rate-limit { type decimal64 { fraction-digits 2; } description "rate-limit action."; } } }

augment "/ietf-acl:access-lists/ietf-acl:acl/ietf-acl:access-list-entries/ietf-acl:ace" {

description "handle non-intial and initial fragments";

leaf fragments { type empty; description "handle fragments."; } }} <CODE ENDS>



3.2. Identifiers

3.2.1. Create Identifiers

A POST request is used to create identifiers, such as names or aliases, for resources for which a mitigation may be requested. Such identifiers may then be used in subsequent DOTS signal channel exchanges to refer more efficiently to the resources under attack (Figure 3).

POST /restconf/data/ietf-dots-data-channel-identifier HTTP/1.1 Host: {host}:{port} Content-Format: "application/yang.api+json" { "ietf-dots-data-channel-identifier:identifier": { "alias": [ { "alias-name": "string", "ip": [ "string" ], "prefix": [ "string" ], "port-range": [ { "lower-port": integer, "upper-port": integer } ], "traffic-protocol": [ integer ], "fqdn": [ "string" ], "uri": [ "string" ] } ] } }

Figure 3: POST to create identifiers

The header parameters are described below:



alias-name: Name of the alias. This is a mandatory attribute.

traffic-protocol: Internet Protocol numbers. This is an optional attribute.

port-range: The port range, lower-port for lower port number and upper-port for upper port number. For TCP, UDP, SCTP, or DCCP: the range of ports (e.g., 80 to 8080). This is an optional attribute.

ip: IP addresses are separated by commas. This is an optional attribute.

prefix: Prefixes are separated by commas. This is an optional attribute.

fqdn: Fully Qualified Domain Name, is the full name of a system, rather than just its hostname. For example, "venera" is a hostname, and "venera.isi.edu" is an FQDN. This is an optional attribute.

uri: Uniform Resource Identifier (URI). This is an optional attribute.

In the POST request at least one of the attributes ip or prefix or fqdn or uri MUST be present. DOTS agents can safely ignore Vendor- Specific parameters they don’t understand.

Figure 4 shows a POST request to create alias called "https1" for HTTP(S) servers with IP addresses 2001:db8:6401::1 and 2001:db8:6401::2 listening on port 443.



POST /restconf/data/ietf-dots-data-channel-identifier HTTP/1.1 Host: www.example.com Content-Format: "application/yang.api+json" { "ietf-dots-data-channel-identifier:identifier": { "alias": [ { "alias-name": "Server1", "traffic-protocol": [ 6 ], "ip": [ "2001:db8:6401::1", "2001:db8:6401::2" ], "port-range": [ { "lower-port": 443 } ] } ] } }

Figure 4: POST to create identifiers

The DOTS server indicates the result of processing the POST request using HTTP response codes. HTTP 2xx codes are success, HTTP 4xx codes are some sort of invalid requests and 5xx codes are returned if the DOTS server has erred or it is incapable of accepting the alias. Response code 201 (Created) will be returned in the response if the DOTS server has accepted the alias. If the request is missing one or more mandatory attributes then 400 (Bad Request) will be returned in the response or if the request contains invalid or unknown parameters then 400 (Invalid query) will be returned in the response. The HTTP response will include the JSON body received in the request.

The DOTS client can use the PUT request (Section 4.5 in [RFC8040]) to create or modify the aliases in the DOTS server.

3.2.2. Delete Identifiers

A DELETE request is used to delete identifiers maintained by a DOTS server (Figure 5).



DELETE /restconf/data/ietf-dots-data-channel-identifier:identifier\ /alias=Server1 HTTP/1.1 Host: {host}:{port}

Figure 5: DELETE identifier

In RESTCONF, URI-encoded path expressions are used. A RESTCONF data resource identifier is encoded from left to right, starting with the top-level data node, according to the "api-path" rule defined in Section 3.5.3.1 of [RFC8040]. The data node in the above path expression is a YANG list node and MUST be encoded according to the rules defined in Section 3.5.1 of [RFC8040].

If the DOTS server does not find the alias name conveyed in the DELETE request in its configuration data, then it responds with a 404 (Not Found) error response code. The DOTS server successfully acknowledges a DOTS client’s request to remove the identifier using 204 (No Content) in the response.

3.2.3. Retrieving Installed Identifiers

A GET request is used to retrieve the set of installed identifiers from a DOTS server (Section 3.3.1 in [RFC8040]). Figure 6 shows how to retrieve all the identifiers that were instantiated by the DOTS client. The content parameter and its permitted values are defined in Section 4.8.1 of [RFC8040].

GET /restconf/data/ietf-dots-data-channel-identifier:identifier?\ content=config HTTP/1.1 Host: {host}:{port} Accept: application/yang-data+json

Figure 6: GET to retrieve all the installed identifiers

Figure 7 shows response for all identifiers on the DOTS server.



{ "ietf-dots-data-channel-identifier:identifier": [ { "alias": [ { "alias-name": "Server1", "traffic-protocol": [ 6 ], "ip": [ "2001:db8:6401::1", "2001:db8:6401::2" ], "port-range": [ { "lower-port": 443 } ] } ] }, { "alias": [ { "alias-name": "Server2", "traffic-protocol": [ 6 ], "ip": [ "2001:db8:6401::10", "2001:db8:6401::20" ], "port-range": [ { "lower-port": 80 } ] } ] } ] }

Figure 7: Response body

If the DOTS server does not find the alias name conveyed in the GET request in its configuration data, then it responds with a 404 (Not Found) error response code.



3.3. Filtering Rules

The DOTS server either receives the filtering rules directly from the DOTS client or via the DOTS gateway. If the DOTS client signals the filtering rules via the DOTS gateway then the DOTS gateway validates if the DOTS client is authorized to signal the filtering rules and if the client is authorized propagates the rules to the DOTS server. Likewise, the DOTS server validates if the DOTS gateway is authorized to signal the filtering rules. To create or purge filters, the DOTS client sends HTTP requests to the DOTS gateway. The DOTS gateway validates the rules in the requests and proxies the requests containing the filtering rules to a DOTS server. When the DOTS gateway receives the associated HTTP response from the DOTS server, it propagates the response back to the DOTS client.

The following APIs define means for a DOTS client to configure filtering rules on a DOTS server.

3.3.1. Install Filtering Rules

A POST request is used to push filtering rules to a DOTS server. Figure 8 shows a POST request example to block traffic from 192.0.2.0/24, destined to 198.51.100.0/24. The ACL JSON configuration for the filtering rule is generated using the ACL YANG data model defined in [I-D.ietf-netmod-acl-model] and the ACL configuration XML for the filtering rule is specified in Section 4.3 of [I-D.ietf-netmod-acl-model].



POST /restconf/data/ietf-access-control-list HTTP/1.1 Host: www.example.com Content-Format: "application/yang.api+json" { "ietf-access-control-list:access-lists": { "acl": [ { "acl-name": "sample-ipv4-acl", "acl-type": "ipv4", "access-list-entries": { "ace": [ { "rule-name": "rule1", "matches": { "source-ipv4-network": "192.0.2.0/24", "destination-ipv4-network": "198.51.100.0/24" }, "actions": { "deny": [null] } } ] } } ] } }

Figure 8: POST to install filterng rules

The header parameters defined in [I-D.ietf-netmod-acl-model] are discussed below:

acl-name: The name of access-list. This is a mandatory attribute.

acl-type: Indicates the primary intended type of match criteria (e.g. IPv4, IPv6). This is a mandatory attribute.

protocol: Internet Protocol numbers. This is an optional attribute.

source-ipv4-network: The source IPv4 prefix. This is an optional attribute.

destination-ipv4-network: The destination IPv4 prefix. This is an optional attribute.



actions: "deny" or "permit" or "rate-limit". "permit" action is used to white-list traffic. "deny" action is used to black-list traffic. "rate-limit" action is used to rate-limit traffic, the allowed traffic rate is represented in bytes per second indicated in IEEE floating point format [IEEE.754.1985]. If actions attribute is not specified in the request then the default action is "deny". This is an optional attribute.

The DOTS server indicates the result of processing the POST request using HTTP response codes. HTTP 2xx codes are success, HTTP 4xx codes are some sort of invalid requests and 5xx codes are returned if the DOTS server has erred or it is incapable of configuring the filtering rules. Response code 201 (Created) will be returned in the response if the DOTS server has accepted the filtering rules. If the request is missing one or more mandatory attributes then 400 (Bad Request) will be returned in the response or if the request contains invalid or unknown parameters then 400 (Invalid query) will be returned in the response.

The DOTS client can use the PUT request to create or modify the filtering rules in the DOTS server.

3.3.2. Remove Filtering Rules

A DELETE request is used to delete filtering rules from a DOTS server (Figure 9).

DELETE /restconf/data/ietf-access-control-list:access-lists/acl-name\ =sample-ipv4-acl&acl-type=ipv4 HTTP/1.1 Host: {host}:{port}

Figure 9: DELETE to remove the filtering rules

If the DOTS server does not find the access list name and access list type conveyed in the DELETE request in its configuration data, then it responds with a 404 (Not Found) error response code. The DOTS server successfully acknowledges a DOTS client’s request to withdraw the filtering rules using 204 (No Content) response code, and removes the filtering rules as soon as possible.

3.3.3. Retrieving Installed Filtering Rules

The DOTS client periodically queries the DOTS server to check the counters for installed filtering rules. A GET request is used to retrieve filtering rules from a DOTS server. Figure 10 shows how to retrieve all the filtering rules programmed by the DOTS client and the number of matches for the installed filtering rules.



GET /restconf/data/ietf-access-control-list:access-lists?content=all HTTP/1.1 Host: {host}:{port} Accept: application/yang-data+json

Figure 10: GET to retrieve the configuration data and state data for the filtering rules

If the DOTS server does not find the access list name and access list type conveyed in the GET request in its configuration data, then it responds with a 404 (Not Found) error response code.


This specification registers new parameters for the DOTS data channel and establishes registries for mappings to JSON attributes.

4.1. DOTS Data Channel JSON Attribute Mappings Registry

A new registry will be requested from IANA, entitled "DOTS data channel JSON attribute Mappings Registry". The registry is to be created as Expert Review Required.

4.2. Registration Template

JSON Attribute: JSON attribute name.

Description: Brief description of the attribute.

Change Controller: For Standards Track RFCs, list the "IESG". For others, give the name of the responsible party. Other details (e.g., postal address, email address, home page URI) may also be included.

Specification Document(s): Reference to the document or documents that specify the parameter, preferably including URIs that can be used to retrieve copies of the documents. An indication of the relevant sections may also be included but is not required.

4.3. Initial Registry Contents

o JSON Attribute: "alias-name" o Description: Name of alias. o Change Controller: IESG o Specification Document(s): this document



o JSON Attribute: "traffic-protocol" o Description: Internet protocol numbers. o Change Controller: IESG o Specification Document(s): this document

o JSON Attribute: "port-range" o Description: The port range, lower-port for lower port number and upper-port for upper port number. For TCP, UDP, SCTP, or DCCP: the range of ports (e.g., 80 to 8080). o Change Controller: IESG o Specification Document(s): this document

o JSON Attribute: "lower-port" o Description: Lower port number for port range. o Change Controller: IESG o Specification Document(s): this document

o JSON Attribute: "upper-port" o Description: Upper port number for port range. o Change Controller: IESG o Specification Document(s): this document

o JSON Attribute: "ip" o Description: IP address. o Change Controller: IESG o Specification Document(s): this document

o JSON Attribute: "prefix" o Description: IP prefix o Change Controller: IESG o Specification Document(s): this document

o JSON Attribute: "fqdn" o Description: Fully Qualified Domain Name, is the full name of a system, rather than just its hostname. For example, "venera" is a hostname, and "venera.isi.edu" is an FQDN. o Change Controller: IESG o Specification Document(s): this document

o JSON Attribute: "uri" o Description: Uniform Resource Identifier (URI). o Change Controller: IESG o Specification Document(s): this document



5. Contributors

The following individuals have contributed to this document:

Dan Wing



Authenticated encryption MUST be used for data confidentiality and message integrity. TLS based on client certificate MUST be used for mutual authentication. The interaction between the DOTS agents requires Transport Layer Security (TLS) with a cipher suite offering confidentiality protection and the guidance given in [RFC7525] MUST be followed to avoid attacks on TLS.

An attacker may be able to inject RST packets, bogus application segments, etc., regardless of whether TLS authentication is used. Because the application data is TLS protected, this will not result in the application receiving bogus data, but it will constitute a DoS on the connection. This attack can be countered by using TCP-AO [RFC5925]. If TCP-AO is used, then any bogus packets injected by an attacker will be rejected by the TCP-AO integrity check and therefore will never reach the TLS layer.

Special care should be taken in order to ensure that the activation of the proposed mechanism won’t have an impact on the stability of the network (including connectivity and services delivered over that network).

Involved functional elements in the cooperation system must establish exchange instructions and notification over a secure and authenticated channel. Adequate filters can be enforced to avoid that nodes outside a trusted domain can inject request such as deleting filtering rules. Nevertheless, attacks can be initiated from within the trusted domain if an entity has been corrupted. Adequate means to monitor trusted nodes should also be enabled.

7. Acknowledgements

Thanks to Christian Jacquenet, Roland Dobbins, Andrew Mortensen, Roman Danyliw, Ehud Doron, Russ White and Gilbert Clark for the discussion and comments.



8. References



[I-D.ietf-netmod-acl-model] Bogdanovic, D., Jethanandani, M., Huang, L., Agarwal, S., and D. Blair, "Network Access Control List (ACL) YANG Data Model", draft-ietf-netmod-acl-model-11 (work in progress), June 2017.



[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP Authentication Option", RFC 5925, DOI 10.17487/RFC5925, June 2010, <http://www.rfc-editor.org/info/rfc5925>.

[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014, <http://www.rfc-editor.org/info/rfc7230>.

[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, "Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 2015, <http://www.rfc-editor.org/info/rfc7525>.

[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG", RFC 7951, DOI 10.17487/RFC7951, August 2016, <http://www.rfc-editor.org/info/rfc7951>.



[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, <http://www.rfc-editor.org/info/rfc8040>.



[I-D.ietf-dots-signal-channel] Reddy, T., Boucadair, M., Patil, P., Mortensen, A., and N. Teague, "Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel", draft-ietf-dots-signal- channel-02 (work in progress), June 2017.

[IEEE.754.1985] Institute of Electrical and Electronics Engineers, "Standard for Binary Floating-Point Arithmetic", August 1985.

[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, <http://www.rfc-editor.org/info/rfc6020>.

[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, <http://www.rfc-editor.org/info/rfc6241>.

[RFC6520] Seggelmann, R., Tuexen, M., and M. Williams, "Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) Heartbeat Extension", RFC 6520, DOI 10.17487/RFC6520, February 2012, <http://www.rfc-editor.org/info/rfc6520>.

[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 2014, <http://www.rfc-editor.org/info/rfc7159>.

[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, <http://www.rfc-editor.org/info/rfc7950>.








Kaname Nishizuka NTT Communications GranPark 16F 3-4-1 Shibaura, Minato-ku Tokyo 108-8118 Japan


Liang Xia Huawei 101 Software Avenue, Yuhuatai District Nanjing, Jiangsu 210012 China






Andrew Mortensen Arbor Networks, Inc. 2727 S. State St Ann Arbor, MI 48104 United States


Nik Teague Verisign, Inc. United States



DOTS M. Boucadair, Ed.Internet-Draft OrangeIntended status: Standards Track T. Reddy, Ed.Expires: January 23, 2020 McAfee July 22, 2019

Distributed Denial-of-Service Open Threat Signaling (DOTS) Data Channel Specification draft-ietf-dots-data-channel-31

Abstract

The document specifies a Distributed Denial-of-Service Open Threat Signaling (DOTS) data channel used for bulk exchange of data that cannot easily or appropriately communicated through the DOTS signal channel under attack conditions.

This is a companion document to the DOTS signal channel specification.

Editorial Note (To be removed by RFC Editor)

Please update these statements within the document with the RFC number to be assigned to this document:

o "This version of this YANG module is part of RFC XXXX;"

o "RFC XXXX: Distributed Denial-of-Service Open Threat Signaling (DOTS) Data Channel Specification";

o reference: RFC XXXX

Please update the "revision" date of the YANG module.

Status of This Memo



Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any

Boucadair & Reddy Expires January 23, 2020 [Page 1]

Internet-Draft DOTS Data Channel Protocol July 2019

time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."


Copyright Notice



Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. DOTS Data Channel . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Design Overview . . . . . . . . . . . . . . . . . . . . . 5 3.2. DOTS Server(s) Discovery . . . . . . . . . . . . . . . . 8 3.3. DOTS Gateways . . . . . . . . . . . . . . . . . . . . . . 8 3.4. Detect and Prevent Infinite Loops . . . . . . . . . . . . 9 3.5. Stale Entries . . . . . . . . . . . . . . . . . . . . . . 10 4. DOTS Data Channel YANG Module . . . . . . . . . . . . . . . . 10 4.1. Generic Tree Structure . . . . . . . . . . . . . . . . . 10 4.2. Filtering Fields . . . . . . . . . . . . . . . . . . . . 13 4.3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 20 5. Managing DOTS Clients . . . . . . . . . . . . . . . . . . . . 37 5.1. Registering DOTS Clients . . . . . . . . . . . . . . . . 37 5.2. Unregistering DOTS Clients . . . . . . . . . . . . . . . 40 6. Managing DOTS Aliases . . . . . . . . . . . . . . . . . . . . 40 6.1. Create Aliases . . . . . . . . . . . . . . . . . . . . . 41 6.2. Retrieve Installed Aliases . . . . . . . . . . . . . . . 45 6.3. Delete Aliases . . . . . . . . . . . . . . . . . . . . . 47 7. Managing DOTS Filtering Rules . . . . . . . . . . . . . . . . 47 7.1. Retrieve DOTS Filtering Capabilities . . . . . . . . . . 47 7.2. Install Filtering Rules . . . . . . . . . . . . . . . . . 49 7.3. Retrieve Installed Filtering Rules . . . . . . . . . . . 52 7.4. Remove Filtering Rules . . . . . . . . . . . . . . . . . 59 8. Operational Considerations . . . . . . . . . . . . . . . . . 60 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 60



10. Security Considerations . . . . . . . . . . . . . . . . . . . 61 11. Contributing Authors . . . . . . . . . . . . . . . . . . . . 63 12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 64 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 65 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 65 14.1. Normative References . . . . . . . . . . . . . . . . . . 65 14.2. Informative References . . . . . . . . . . . . . . . . . 66 Appendix A. Sample Examples: Filtering Fragments . . . . . . . . 68 Appendix B. Sample Examples: Filtering TCP Messages . . . . . . 71 B.1. Discard TCP Null Attack . . . . . . . . . . . . . . . . . 71 B.2. Rate-Limit SYN Flooding . . . . . . . . . . . . . . . . . 72 B.3. Rate-Limit ACK Flooding . . . . . . . . . . . . . . . . . 73 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 74

1. Introduction

A distributed denial-of-service (DDoS) attack is an attempt to make machines or network resources unavailable to their intended users. In most cases, sufficient scale can be achieved by compromising enough end-hosts and using those infected hosts to perpetrate and amplify the attack. The victim of such attack can be an application server, a router, a firewall, an entire network, etc.

As discussed in [RFC8612], the lack of a common method to coordinate a real-time response among involved actors and network domains inhibits the speed and effectiveness of DDoS attack mitigation. From that standpoint, DDoS Open Threat Signaling (DOTS) defines an architecture that allows a DOTS client to send requests to a DOTS server for DDoS attack mitigation [I-D.ietf-dots-architecture]. The DOTS approach is thus meant to minimize the impact of DDoS attacks, thereby contributing to the enforcement of more efficient defensive if not proactive security strategies. To that aim, DOTS defines two channels: the signal and the data channels (Figure 1).


Figure 1: DOTS Channels

The DOTS signal channel is used to carry information about a device or a network (or a part thereof) that is under a DDoS attack. Such information is sent by a DOTS client to an upstream DOTS server so that appropriate mitigation actions are undertaken on traffic deemed suspicious. The DOTS signal channel is further elaborated in [I-D.ietf-dots-signal-channel].



As for the DOTS data channel, it is used for infrequent bulk data exchange between DOTS agents to significantly improve the coordination of all the parties involved in the response to the attack. Section 2 of [I-D.ietf-dots-architecture] mentions that the DOTS data channel is used to perform the following tasks:

o Creating aliases for resources for which mitigation may be requested.

A DOTS client may submit to its DOTS server a collection of prefixes which it would like to refer to by an alias when requesting mitigation. The DOTS server can respond to this request with either a success or failure response (see Section 2 in [I-D.ietf-dots-architecture]).

Refer to Section 6 for more details.

o Policy management, which enables a DOTS client to request the installation or withdrawal of traffic filters, dropping or rate- limiting unwanted traffic, and permitting accept-listed traffic. A DOTS client is entitled to instruct filtering rules only on IP resources that belong to its domain.

Sample use cases for populating drop- or accept-list filtering rules are detailed hereafter:

* If a network resource (DOTS client) is informed about a potential DDoS attack from a set of IP addresses, the DOTS client informs its servicing DOTS gateway of all suspect IP addresses that need to be drop-listed for further investigation. The DOTS client could also specify a list of protocols and port numbers in the drop-list rule.

The DOTS gateway then propagates the drop-listed IP addresses to a DOTS server which will undertake appropriate actions so that traffic originated by these IP addresses to the target network (specified by the DOTS client) is blocked.

* A network, that has partner sites from which only legitimate traffic arrives, may want to ensure that the traffic from these sites is not subjected to DDoS attack mitigation. The DOTS client uses the DOTS data channel to convey the accept-listed IP prefixes of the partner sites to its DOTS server.

The DOTS server uses this information to accept-list flows originated by such IP prefixes and which reach the network.

Refer to Section 7 for more details.



2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

The reader should be familiar with the terms defined in [RFC8612].

The terminology for describing YANG modules is defined in [RFC7950]. The meaning of the symbols in the tree diagrams is defined in [RFC8340].

This document generalizes the notion of Access Control List (ACL) so that it is not device-specific [RFC8519]. As such, this document defines an ACL as an ordered set of rules that is used to filter traffic. Each rule is represented by an Access Control Entry (ACE). ACLs communicated via the DOTS data channel are not bound to a device interface.

For the sake of simplicity, all of the examples in this document use "/restconf" as the discovered RESTCONF API root path. Many protocol header lines and message-body text within examples throughout the document are split into multiple lines for display purposes only. When a line ends with backslash (’\’) as the last character, the line is wrapped for display purposes. It is to be considered to be joined to the next line by deleting the backslash, the following line break, and the leading whitespace of the next line.

3. DOTS Data Channel

3.1. Design Overview

Unlike the DOTS signal channel, which must remain operational even when confronted with signal degradation due to packets loss, the DOTS data channel is not expected to be fully operational at all times, especially when a DDoS attack is underway. The requirements for a DOTS data channel protocol are documented in [RFC8612].

This specification does not require an order of DOTS signal and data channel creations nor mandates a time interval between them. These considerations are implementation- and deployment-specific.

As the primary function of the data channel is data exchange, a reliable transport mode is required in order for DOTS agents to detect data delivery success or failure. This document uses RESTCONF



[RFC8040] over TLS over TCP as the DOTS data channel protocol. The abstract layering of DOTS data channel is shown in Figure 2.

+-------------------+ | DOTS Data Channel | +-------------------+ | RESTCONF | +-------------------+ | TLS | +-------------------+ | TCP | +-------------------+ | IP | +-------------------+

Figure 2: Abstract Layering of DOTS Data Channel

The HTTP POST, PUT, PATCH, and DELETE methods are used to edit data resources represented by DOTS data channel YANG modules. These basic edit operations allow the DOTS data channel running configuration to be altered by a DOTS client. Rules for generating and processing RESTCONF methods are defined in Section 4 of [RFC8040].

DOTS data channel configuration information as well as state information can be retrieved with the GET method. An HTTP status- line is returned for each request to report success or failure for RESTCONF operations (Section 5.4 of [RFC8040]). The "error-tag" provides more information about encountered errors (Section 7 of [RFC8040]).

DOTS clients perform the root resource discovery procedure discussed in Section 3.1 of [RFC8040] to determine the root of the RESTCONF API. After discovering the RESTCONF API root, a DOTS client uses this value as the initial part of the path in the request URI in any subsequent request to the DOTS server. The DOTS server may support the retrieval of the YANG modules it supports (Section 3.7 in [RFC8040]). For example, a DOTS client may use RESTCONF to retrieve the vendor-specific YANG modules supported by its DOTS server.

JavaScript Object Notation (JSON) [RFC8259] payloads are used to propagate the DOTS data-channel-specific payload messages that carry request parameters and response information, such as errors. This specification uses the encoding rules defined in [RFC7951] for representing DOTS data channel configuration data using YANG (Section 4) as JSON text.

A DOTS client registers itself to its DOTS server(s) in order to set up DOTS data channel-related configuration data and receive state



data (i.e., non-configuration data) from the DOTS server(s) (Section 5). Mutual authentication considerations are specified in Section 8 of [I-D.ietf-dots-signal-channel]. The coupling of signal and data channels is discussed in Section 4.4.1 of [I-D.ietf-dots-signal-channel].

A DOTS client can either maintain a persistent connection or periodic connections with its DOTS server(s). If the DOTS client needs to frequently update the drop-list or accept-list filtering rules or aliases, it maintains a persistent connection with the DOTS server. For example, CAPTCHA and cryptographic puzzles can be used by the mitigation service in the DOTS client domain to determine whether the IP address is used for legitimate purpose or not, and the DOTS client can frequently update the drop-list filtering rules. A persistent connection is also useful if the DOTS client subscribes to event notifications (Section 6.3 of [RFC8040]). Additional considerations related to RESTCONF connection management (including, configuring the connection type or the reconnect strategy) can be found in [I-D.ietf-netconf-restconf-client-server].

A single DOTS data channel between DOTS agents can be used to exchange multiple requests and multiple responses. To reduce DOTS client and DOTS server workload, DOTS clients SHOULD re-use the same TLS session. While the communication to the DOTS server is quiescent, the DOTS client MAY probe the server to ensure it has maintained cryptographic state. Such probes can also keep alive firewall and/or NAT bindings. A TLS heartbeat [RFC6520] verifies that the DOTS server still has TLS state by returning a TLS message.

A DOTS server may detect conflicting filtering requests from distinct DOTS clients which belong to the same domain. For example, a DOTS client could request to drop-list a prefix by specifying the source prefix, while another DOTS client could request to accept-list that same source prefix, but both having the same destination prefix. DOTS servers SHOULD support a configuration parameter to indicate the behavior to follow when a conflict is detected (e.g., reject all, reject the new request, notify an administrator for validation). Section 7.2 specifies a default behavior when no instruction is supplied to a DOTS server.

How a DOTS client synchronizes its configuration with the one maintained by its DOTS server(s) is implementation-specific. For example:

o a DOTS client can systematically send a GET message before and/or after a configuration change request.



o a DOTS client can re-establish the disconnected DOTS session after an attack is mitigated and sends a GET message before a configuration change request.

NAT considerations for the DOTS data channel are similar to those discussed in Section 3 of [I-D.ietf-dots-signal-channel].

How filtering rules that are instantiated on a DOTS server are translated into network configurations actions is out of scope of this specification.

Some of the fields introduced in Section 4 are also discussed in Sections 5, 6, and 7. These sections are authoritative for these fields.

3.2. DOTS Server(s) Discovery

This document assumes that DOTS clients are provisioned with a way to know how to reach their DOTS server(s), which could occur by a variety of means (e.g., local configuration, or dynamic means such as DHCP [I-D.ietf-dots-server-discovery]). The specification of such means are out of scope of this document.

Likewise, it is out of scope of this document to specify the behavior to be followed by a DOTS client to send DOTS requests when multiple DOTS servers are provisioned (e.g., contact all DOTS servers, select one DOTS server among the list).

3.3. DOTS Gateways

When a server-domain DOTS gateway is involved in DOTS data channel exchanges, the same considerations for manipulating the ’cdid’ (client domain identifier) parameter specified in [I-D.ietf-dots-signal-channel] MUST be followed by DOTS agents. As a reminder, ’cdid’ is meant to assist the DOTS server to enforce some policies (e.g., limit the number of filtering rules per DOTS client or per DOTS client domain). A loop detect mechanism for DOTS gateways is specified in Section 3.4.

If a DOTS gateway is involved, the DOTS gateway verifies that the DOTS client is authorized to undertake a data channel action (e.g., instantiate filtering rules). If the DOTS client is authorized, it propagates the rules to the upstream DOTS server. Likewise, the DOTS server verifies that the DOTS gateway is authorized to relay data channel actions. For example, to create or purge filters, a DOTS client sends its request to its DOTS gateway. The DOTS gateway validates the rules in the request and proxies the requests containing the filtering rules to its DOTS server. When the DOTS



gateway receives the associated response from the DOTS server, it propagates the response back to the DOTS client.

3.4. Detect and Prevent Infinite Loops

In order to detect and prevent infinite loops, DOTS gateways MUST support the procedure defined in Section 5.7.1 of [RFC7230]. In particular, each intermediate DOTS gateway MUST check that none of its own information (e.g., server names, literal IP addresses) is present in the "Via" header field of a DOTS message it receives:

o If it detects that its own information is present in the "Via" header field, the DOTS gateway MUST NOT forward the DOTS message. Messages that cannot be forwarded because of a loop SHOULD be logged with a "508 Loop Detected" status-line returned sent back to the DOTS peer. The structure of the reported error is depicted in Figure 3.

error-app-tag: loop-detected error-tag: operation-failed error-type: transport, application error-info: <via-header> : A copy of the Via header field when the loop was detected. Description: An infinite loop has been detected when forwarding a requests via a proxy.

Figure 3: Loop Detected Error

It is RECOMMENDED that DOTS clients and gateways support methods to alert administrators about loop errors so that appropriate actions are undertaken.

o Otherwise, the DOTS agent MUST update or insert the "Via" header by appending its own information.

Unless configured otherwise, DOTS gateways at the boundaries of a DOTS client domain SHOULD remove the previous "Via" header field information after checking for a loop before forwarding. This behavior is required for topology hiding purposes but can also serve to minimize potential conflicts that may arise if overlapping information is used in distinct DOTS domains (e.g., private IPv4 addresses, non globally unique aliases).



3.5. Stale Entries

In order to avoid stale entries, a lifetime is associated with alias and filtering entries created by DOTS clients. Also, DOTS servers may track the inactivity timeout of DOTS clients to detect stale entries.

4. DOTS Data Channel YANG Module

4.1. Generic Tree Structure

The DOTS data channel YANG module (ietf-dots-data-channel) provides a method for DOTS clients to manage aliases for resources for which mitigation may be requested. Such aliases may be used in subsequent DOTS signal channel exchanges to refer more efficiently to the resources under attack.

Note that the full module’s tree has been split across several figures to aid the exposition of the various sub-trees.

The tree structure for the DOTS alias is depicted in Figure 4.

module: ietf-dots-data-channel +--rw dots-data +--rw dots-client* [cuid] | +--rw cuid string | +--rw cdid? string | +--rw aliases | | +--rw alias* [name] | | +--rw name string | | +--rw target-prefix* inet:ip-prefix | | +--rw target-port-range* [lower-port] | | | +--rw lower-port inet:port-number | | | +--rw upper-port? inet:port-number | | +--rw target-protocol* uint8 | | +--rw target-fqdn* inet:domain-name | | +--rw target-uri* inet:uri | | +--ro pending-lifetime? int32 | +--rw acls | ... +--ro capabilities ...

Figure 4: DOTS Alias Subtree

Also, the ’ietf-dots-data-channel’ module provides a method for DOTS clients to manage filtering rules. Examples of filtering management in a DOTS context include, but not limited to:



o Drop-list management, which enables a DOTS client to inform a DOTS server about sources from which traffic should be discarded.

o Accept-list management, which enables a DOTS client to inform a DOTS server about sources from which traffic should always be accepted.

o Policy management, which enables a DOTS client to request the installation or withdrawal of traffic filters, dropping or rate- limiting unwanted traffic and permitting accept-listed traffic.

The tree structure for the DOTS filtering entries is depicted in Figure 5.

Investigations into the prospect of augmenting ’ietf-access-control- list’ to meet DOTS requirements concluded that such a design approach did not support many of the DOTS requirements, e.g.,

o Retrieve a filtering entry (or all entries) created by a DOTS client.

o Delete a filtering entry that was instantiated by a DOTS client.

Accordingly, new DOTS filtering entries (i.e., Access Control List (ACL)) are defined that mimic the structure specified in [RFC8519]. Concretely, DOTS agents are assumed to manipulate an ordered list of ACLs; each ACL contains a separately ordered list of Access Control Entries (ACEs). Each ACE has a group of match and a group of action criteria.

Once all the ACE entries have been iterated though with no match, then all the following ACL’s ACE entries are iterated through until the first match at which point the specified action is applied. If there is no match during ’idle’ time (i.e., no mitigation is active), then there is no further action to be taken against the packet. If there is no match during active mitigation, then the packet will still be scrubbed by the DDoS mitigator.



supported in ’ietf-dots-data-channel’ because it is not appropriate in the context of DDoS mitigation. Generating ICMP messages to notify drops when mitigating a DDoS attack will exacerbate the DDoS attack. Furthermore, these ICMP messages will be used by an attacker as an explicit signal that the traffic is being blocked.

4.2. Filtering Fields

The ’ietf-dots-data-channel’ module reuses the packet fields module ’ietf-packet-fields’ [RFC8519] which defines matching on fields in the packet including IPv4, IPv6, and transport layer fields. The ’ietf-dots-data-channel’ module can be augmented, for example, to support additional protocol-specific matching fields.

This specification defines a new IPv4/IPv6 matching field called ’fragment’ to efficiently handle fragment-related filtering rules. Indeed, [RFC8519] does not support such capability for IPv6 but offers a partial support for IPv4 by means of ’flags’. Nevertheless, the use of ’flags’ is problematic since it does not allow to define a bitmask. For example, setting other bits not covered by the ’flags’ filtering clause in a packet will allow that packet to get through (because it won’t match the ACE). Sample examples to illustrate how ’fragment’ can be used are provided in Appendix A.

Figure 6 shows the IPv4 match subtree.



The following match fields MUST be supported by DOTS implementations (Table 1):

ACL Mandatory Fields Match ------- ------------------------------------------------------------- ipv4 length, protocol, destination-ipv4-network, source- ipv4-network, and fragment ipv6 length, protocol, destination-ipv6-network, source- ipv6-network, and fragment tcp flags-bitmask, source-port-range-or-operator, and destination-port-range-or-operator udp length, source-port-range-or-operator, and destination-port- range-or-operator icmp type and code

Table 1: Mandatory DOTS Channel Match Fields

Implementations MAY support other filtering match fields and actions. The ’ietf-dots-data-channel’ provides a method for an implementation to expose its filtering capabilities. The tree structure of the ’capabilities’ is shown in Figure 10. DOTS clients that support both ’fragment’ and ’flags’ (or ’flags-bitmask’ and ’flags’) matching fields MUST NOT set these fields in the same request.

module: ietf-dots-data-channel +--rw dots-data ... +--ro capabilities +--ro address-family* enumeration +--ro forwarding-actions* identityref +--ro rate-limit? boolean +--ro transport-protocols* uint8 +--ro ipv4 | +--ro dscp? boolean | +--ro ecn? boolean | +--ro length? boolean | +--ro ttl? boolean | +--ro protocol? boolean | +--ro ihl? boolean | +--ro flags? boolean | +--ro offset? boolean | +--ro identification? boolean | +--ro source-prefix? boolean | +--ro destination-prefix? boolean | +--ro fragment? boolean +--ro ipv6 | +--ro dscp? boolean



| +--ro ecn? boolean | +--ro length? boolean | +--ro hoplimit? boolean | +--ro protocol? boolean | +--ro destination-prefix? boolean | +--ro source-prefix? boolean | +--ro flow-label? boolean | +--ro fragment? boolean +--ro tcp | +--ro sequence-number? boolean | +--ro acknowledgement-number? boolean | +--ro data-offset? boolean | +--ro reserved? boolean | +--ro flags? boolean | +--ro window-size? boolean | +--ro urgent-pointer? boolean | +--ro options? boolean | +--ro flags-bitmask? boolean | +--ro source-port? boolean | +--ro destination-port? boolean | +--ro port-range? boolean +--ro udp | +--ro length? boolean | +--ro source-port? boolean | +--ro destination-port? boolean | +--ro port-range? boolean +--ro icmp +--ro type? boolean +--ro code? boolean +--ro rest-of-header? boolean

Figure 10: Filtering Capabilities Subtree

4.3. YANG Module

This module uses the common YANG types defined in [RFC6991] and types defined in [RFC8519].

<CODE BEGINS> file "[email protected]" module ietf-dots-data-channel { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-dots-data-channel"; prefix data-channel;

import ietf-inet-types { prefix inet; reference "Section 4 of RFC 6991"; }



import ietf-access-control-list { prefix ietf-acl; reference "RFC 8519: YANG Data Model for Network Access Control Lists (ACLs)"; } import ietf-packet-fields { prefix packet-fields; reference "RFC 8519: YANG Data Model for Network Access Control Lists (ACLs)"; }

organization "IETF DDoS Open Threat Signaling (DOTS) Working Group"; contact "WG Web: <https://datatracker.ietf.org/wg/dots/> WG List: <mailto:[email protected]>

Editor: Mohamed Boucadair <mailto:[email protected]>

Editor: Konda, Tirumaleswar Reddy <mailto:[email protected]>

Author: Jon Shallow <mailto:[email protected]>

Author: Kaname Nishizuka <mailto:[email protected]>

Author: Liang Xia <mailto:[email protected]>

Author: Prashanth Patil <mailto:[email protected]>

Author: Andrew Mortensen <mailto:[email protected]>

Author: Nik Teague <mailto:[email protected]>"; description "This module contains YANG definition for configuring aliases for resources and filtering rules using DOTS data channel.

Copyright (c) 2019 IETF Trust and the persons identified as



authors of the code. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust’s Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info).

This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices.";

revision 2019-05-09 { description "Initial revision."; reference "RFC XXXX: Distributed Denial-of-Service Open Threat Signaling (DOTS) Data Channel Specification"; }

typedef activation-type { type enumeration { enum "activate-when-mitigating" { value 1; description "The Access Control List (ACL) is installed only when a mitigation is active for the DOTS client."; } enum "immediate" { value 2; description "The ACL is immediately activated."; } enum "deactivate" { value 3; description "The ACL is maintained by the DOTS server, but it is deactivated."; } } description "Indicates the activation type of an ACL."; }

typedef operator { type bits { bit not { position 0;



description "If set, logical negation of operation."; } bit match { position 1; description "Match bit. This is a bitwise match operation defined as ’(data & value) == value’."; } bit any { position 3; description "Any bit. This is a match on any of the bits in bitmask. It evaluates to ’true’ if any of the bits in the value mask are set in the data, i.e., ’(data & value) != 0’."; } } description "Specifies how to apply the defined bitmask."; }

grouping tcp-flags { leaf operator { type operator; default "match"; description "Specifies how to interpret the TCP flags."; } leaf bitmask { type uint16; mandatory true; description "The bitmask matches the last 4 bits of byte 12 and byte 13 of the TCP header. For clarity, the 4 bits of byte 12 corresponding to the TCP data offset field are not included in any matching."; } description "Operations on TCP flags."; }

typedef fragment-type { type bits { bit df { position 0; description "Don’t fragment bit for IPv4.



Must be set to 0 when it appears in an IPv6 filter."; } bit isf { position 1; description "Is a fragment."; } bit ff { position 2; description "First fragment."; } bit lf { position 3; description "Last fragment."; } } description "Different fragment types to match against."; }

grouping target { description "Specifies the targets of the mitigation request."; leaf-list target-prefix { type inet:ip-prefix; description "IPv4 or IPv6 prefix identifying the target."; } list target-port-range { key "lower-port"; description "Port range. When only lower-port is present, it represents a single port number."; leaf lower-port { type inet:port-number; mandatory true; description "Lower port number of the port range."; } leaf upper-port { type inet:port-number; must ’. >= ../lower-port’ { error-message "The upper port number must be greater than or equal to the lower-port number."; }



description "Upper port number of the port range."; } } leaf-list target-protocol { type uint8; description "Identifies the target protocol number.

Values are taken from the IANA protocol registry: https://www.iana.org/assignments/protocol-numbers/ protocol-numbers.xhtml

For example, 6 for TCP or 17 for UDP."; } leaf-list target-fqdn { type inet:domain-name; description "FQDN identifying the target."; } leaf-list target-uri { type inet:uri; description "URI identifying the target."; } }

grouping fragment-fields { leaf operator { type operator; default "match"; description "Specifies how to interpret the fragment type."; } leaf type { type fragment-type; mandatory true; description "Indicates what fragment type to look for."; } description "Operations on fragment types."; }

grouping aliases { description "Top level container for aliases."; list alias {



key "name"; description "List of aliases."; leaf name { type string; description "The name of the alias."; } uses target; leaf pending-lifetime { type int32; units "minutes"; config false; description "Indicates the pending validity lifetime of the alias entry."; } } }

grouping ports { choice source-port { container source-port-range-or-operator { uses packet-fields:port-range-or-operator; description "Source port definition."; } description "Choice of specifying the source port or referring to a group of source port numbers."; } choice destination-port { container destination-port-range-or-operator { uses packet-fields:port-range-or-operator; description "Destination port definition."; } description "Choice of specifying a destination port or referring to a group of destination port numbers."; } description "Choice of specifying a source or destination port numbers."; }

grouping access-lists { description "Specifies the ordered set of Access Control Lists.";



list acl { key "name"; ordered-by user; description "An ACL is an ordered list of Access Control Entries (ACE). Each ACE has a list of match criteria and a list of actions."; leaf name { type string { length "1..64"; } description "The name of the access list."; reference "RFC 8519: YANG Data Model for Network Access Control Lists (ACLs)"; } leaf type { type ietf-acl:acl-type; description "Type of access control list. Indicates the primary intended type of match criteria (e.g., IPv4, IPv6) used in the list instance."; reference "RFC 8519: YANG Data Model for Network Access Control Lists (ACLs)"; } leaf activation-type { type activation-type; default "activate-when-mitigating"; description "Indicates the activation type of an ACL. An ACL can be deactivated, installed immediately, or installed when a mitigation is active."; } leaf pending-lifetime { type int32; units "minutes"; config false; description "Indicates the pending validity lifetime of the ACL entry."; } container aces { description "The Access Control Entries container contains a list of ACEs."; list ace { key "name";



ordered-by user; description "List of access list entries."; leaf name { type string { length "1..64"; } description "A unique name identifying this ACE."; reference "RFC 8519: YANG Data Model for Network Access Control Lists (ACLs)"; } container matches { description "The rules in this set determine what fields will be matched upon before any action is taken on them.

If no matches are defined in a particular container, then any packet will match that container.

If no matches are specified at all in an ACE, then any packet will match the ACE."; reference "RFC 8519: YANG Data Model for Network Access Control Lists (ACLs)"; choice l3 { container ipv4 { when "derived-from(../../../../type, " + "’ietf-acl:ipv4-acl-type’)"; uses packet-fields:acl-ip-header-fields; uses packet-fields:acl-ipv4-header-fields; container fragment { description "Indicates how to handle IPv4 fragments."; uses fragment-fields; } description "Rule set that matches IPv4 header."; } container ipv6 { when "derived-from(../../../../type, " + "’ietf-acl:ipv6-acl-type’)"; uses packet-fields:acl-ip-header-fields; uses packet-fields:acl-ipv6-header-fields; container fragment { description "Indicates how to handle IPv6 fragments.";



uses fragment-fields; } description "Rule set that matches IPv6 header."; } description "Either IPv4 or IPv6."; } choice l4 { container tcp { uses packet-fields:acl-tcp-header-fields; container flags-bitmask { description "Indicates how to handle TCP flags."; uses tcp-flags; } uses ports; description "Rule set that matches TCP header."; } container udp { uses packet-fields:acl-udp-header-fields; uses ports; description "Rule set that matches UDP header."; } container icmp { uses packet-fields:acl-icmp-header-fields; description "Rule set that matches ICMP/ICMPv6 header."; } description "Can be TCP, UDP, or ICMP/ICMPv6"; } } container actions { description "Definitions of action for this ACE."; leaf forwarding { type identityref { base ietf-acl:forwarding-action; } mandatory true; description "Specifies the forwarding action per ACE."; reference "RFC 8519: YANG Data Model for Network Access Control Lists (ACLs)";



} leaf rate-limit { when "../forwarding = ’ietf-acl:accept’" { description "Rate-limit is valid only when accept action is used."; } type decimal64 { fraction-digits 2; } units "bytes per second"; description "Specifies how to rate-limit the traffic."; } } container statistics { config false; description "Aggregate statistics."; uses ietf-acl:acl-counters; } } } } }

container dots-data { description "Main container for DOTS data channel."; list dots-client { key "cuid"; description "List of DOTS clients."; leaf cuid { type string; description "A unique identifier that is generated by a DOTS client to prevent request collisions."; reference "RFC YYYY: Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification"; } leaf cdid { type string; description "A client domain identifier conveyed by a server-domain DOTS gateway to a remote DOTS server."; reference



"RFC YYYY: Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification"; } container aliases { description "Set of aliases that are bound to a DOTS client."; uses aliases; } container acls { description "Access lists that are bound to a DOTS client."; uses access-lists; } } container capabilities { config false; description "Match capabilities"; leaf-list address-family { type enumeration { enum "ipv4" { description "IPv4 is supported."; } enum "ipv6" { description "IPv6 is supported."; } } description "Indicates the IP address families supported by the DOTS server."; } leaf-list forwarding-actions { type identityref { base ietf-acl:forwarding-action; } description "Supported forwarding action(s)."; } leaf rate-limit { type boolean; description "Support of rate-limit action."; } leaf-list transport-protocols { type uint8; description



"Upper-layer protocol associated with a filtering rule.

Values are taken from the IANA protocol registry: https://www.iana.org/assignments/protocol-numbers/ protocol-numbers.xhtml

For example, this field contains 1 for ICMP, 6 for TCP 17 for UDP, or 58 for ICMPv6."; } container ipv4 { description "Indicates IPv4 header fields that are supported to enforce ACLs."; leaf dscp { type boolean; description "Support of filtering based on Differentiated Services Code Point (DSCP)."; } leaf ecn { type boolean; description "Support of filtering based on Explicit Congestion Notification (ECN)."; } leaf length { type boolean; description "Support of filtering based on the Total Length."; } leaf ttl { type boolean; description "Support of filtering based on the Time to Live (TTL)."; } leaf protocol { type boolean; description "Support of filtering based on protocol field."; } leaf ihl { type boolean; description "Support of filtering based on the Internet Header Length (IHL)."; } leaf flags { type boolean;



description "Support of filtering based on the ’flags’."; } leaf offset { type boolean; description "Support of filtering based on the ’offset’."; } leaf identification { type boolean; description "Support of filtering based on the ’identification’."; } leaf source-prefix { type boolean; description "Support of filtering based on the source prefix."; } leaf destination-prefix { type boolean; description "Support of filtering based on the destination prefix."; } leaf fragment { type boolean; description "Indicates the capability of a DOTS server to enforce filters on IPv4 fragments. That is, the match functionality based on the Layer 3 ’fragment’ clause is supported."; } } container ipv6 { description "Indicates IPv6 header fields that are supported to enforce ACLs."; leaf dscp { type boolean; description "Support of filtering based on DSCP."; } leaf ecn { type boolean; description "Support of filtering based on ECN."; } leaf length { type boolean;



description "Support of filtering based on the Payload Length."; } leaf hoplimit { type boolean; description "Support of filtering based on the Hop Limit."; } leaf protocol { type boolean; description "Support of filtering based on the Next Header field."; } leaf destination-prefix { type boolean; description "Support of filtering based on the destination prefix."; } leaf source-prefix { type boolean; description "Support of filtering based on the source prefix."; } leaf flow-label { type boolean; description "Support of filtering based on the Flow label."; } leaf fragment { type boolean; description "Indicates the capability of a DOTS server to enforce filters on IPv6 fragments."; } } container tcp { description "Set of TCP fields that are supported by the DOTS server to enforce filters."; leaf sequence-number { type boolean; description "Support of filtering based on the TCP sequence number."; } leaf acknowledgement-number { type boolean; description "Support of filtering based on the TCP acknowledgement



number."; } leaf data-offset { type boolean; description "Support of filtering based on the TCP data-offset."; } leaf reserved { type boolean; description "Support of filtering based on the TCP reserved field."; } leaf flags { type boolean; description "Support of filtering, as defined in RFC 8519, based on the TCP flags."; } leaf window-size { type boolean; description "Support of filtering based on the TCP window size."; } leaf urgent-pointer { type boolean; description "Support of filtering based on the TCP urgent pointer."; } leaf options { type boolean; description "Support of filtering based on the TCP options."; } leaf flags-bitmask { type boolean; description "Support of filtering based on the TCP flags bitmask."; } leaf source-port { type boolean; description "Support of filtering based on the source port number."; } leaf destination-port { type boolean; description "Support of filtering based on the destination port number.";



} leaf port-range { type boolean; description "Support of filtering based on a port range.

This includes filtering based on a source port range, destination port range, or both. All operators (i.e, less than or equal to, greater than or equal to, equal to, and not equal to) are supported."; } } container udp { description "Set of UDP fields that are supported by the DOTS server to enforce filters."; leaf length { type boolean; description "Support of filtering based on the UDP length."; } leaf source-port { type boolean; description "Support of filtering based on the source port number."; } leaf destination-port { type boolean; description "Support of filtering based on the destination port number."; } leaf port-range { type boolean; description "Support of filtering based on a port range.

This includes filtering based on a source port range, destination port range, or both. All operators (i.e, less than or equal, greater than or equal, equal to, and not equal to) are supported."; } } container icmp { description "Set of ICMP/ICMPv6 fields that are supported by the DOTS server to enforce filters."; leaf type {



type boolean; description "Support of filtering based on the ICMP/ICMPv6 type."; } leaf code { type boolean; description "Support of filtering based on the ICMP/ICMPv6 code."; } leaf rest-of-header { type boolean; description "Support of filtering based on the ICMP four-bytes field / the ICMPv6 message body."; } } } } } <CODE ENDS>

5. Managing DOTS Clients

5.1. Registering DOTS Clients

In order to make use of DOTS data channel, a DOTS client MUST register to its DOTS server(s) by creating a DOTS client (’dots- client’) resource. To that aim, DOTS clients SHOULD send a POST request (shown in Figure 11).

POST /restconf/data/ietf-dots-data-channel:dots-data HTTP/1.1 Host: {host}:{port} Content-Type: application/yang-data+json

{ "ietf-dots-data-channel:dots-client": [ { "cuid": "string" } ] }

Figure 11: POST to Register Schema

The ’cuid’ (client unique identifier) parameter is described below:

cuid: A globally unique identifier that is meant to prevent collisions among DOTS clients. This attribute has the same



meaning, syntax, and processing rules as the ’cuid’ attribute defined in [I-D.ietf-dots-signal-channel].

DOTS clients MUST use the same ’cuid’ for both signal and data channels.

This is a mandatory attribute.

In deployments where server-domain DOTS gateways are enabled, identity information about the origin source client domain SHOULD be supplied to the DOTS server. That information is meant to assist the DOTS server to enforce some policies. These policies can be enforced per-client, per-client domain, or both. Figure 12 shows a schema example of a request relayed by a server-domain DOTS gateway.

POST /restconf/data/ietf-dots-data-channel:dots-data HTTP/1.1 Host: {host}:{port} Content-Type: application/yang-data+json

{ "ietf-dots-data-channel:dots-client": [ { "cuid": "string", "cdid": "string" } ] }

Figure 12: POST to Register Schema (via a Server-Domain DOTS Gateway)

A server-domain DOTS gateway SHOULD add the following attribute:

cdid: This attribute has the same meaning, syntax, and processing rules as the ’cdid’ attribute defined in [I-D.ietf-dots-signal-channel].

In deployments where server-domain DOTS gateways are enabled, ’cdid’ does not need to be inserted when relaying DOTS methods to manage aliases (Section 6) or filtering rules (Section 7). DOTS servers are responsible for maintaining the association between ’cdid’ and ’cuid’ for policy enforcement purposes.

This is an optional attribute.

A request example to create a ’dots-client’ resource is depicted in Figure 13. This request is relayed by a server-domain DOTS gateway as hinted by the presence of the ’cdid’ attribute.



POST /restconf/data/ietf-dots-data-channel:dots-data HTTP/1.1 Host: example.com Content-Type: application/yang-data+json

{ "ietf-dots-data-channel:dots-client": [ { "cuid": "dz6pHjaADkaFTbjr0JGBpw", "cdid": "7eeaf349529eb55ed50113" } ] }

Figure 13: POST to Register (DOTS gateway)

As a reminder, DOTS gateways may rewrite the ’cuid’ used by peer DOTS clients (Section 4.4.1 of [I-D.ietf-dots-signal-channel]).

DOTS servers can identify the DOTS client domain using the ’cdid’ parameter or using the client’s DNS name specified in the Subject Alternative Name extension’s dNSName type in the client certificate [RFC6125].

DOTS servers MUST limit the number of ’dots-client’ resources to be created by the same DOTS client to 1 per request. Requests with multiple ’dots-client’ resources MUST be rejected by DOTS servers. To that aim, the DOTS server MUST rely on the same procedure to unambiguously identify a DOTS client as discussed in Section 4.4.1 of [I-D.ietf-dots-signal-channel].

The DOTS server indicates the result of processing the POST request using status-line codes. Status codes in the range "2xx" codes are success, "4xx" codes are some sort of invalid requests and "5xx" codes are returned if the DOTS server has erred or is incapable of accepting the creation of the ’dots-client’ resource. In particular,

o "201 Created" status-line is returned in the response, if the DOTS server has accepted the request.

o "400 Bad Request" status-line is returned by the DOTS server, if the request does not include a ’cuid’ parameter. The error-tag "missing-attribute" is used in this case.

o "409 Conflict" status-line is returned to the requesting DOTS client, if the data resource already exists. The error-tag "resource-denied" is used in this case.



Once a DOTS client registers itself to a DOTS server, it can create/delete/retrieve aliases (Section 6) and filtering rules (Section 7).

A DOTS client MAY use the PUT request (Section 4.5 in [RFC8040]) to register a DOTS client within the DOTS server. An example is shown in Figure 14.

PUT /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=dz6pHjaADkaFTbjr0JGBpw HTTP/1.1 Host: example.com Content-Type: application/yang-data+json

{ "ietf-dots-data-channel:dots-client": [ { "cuid": "dz6pHjaADkaFTbjr0JGBpw" } ] }

Figure 14: PUT to Register

The DOTS gateway that inserted a ’cdid’ in a PUT request MUST strip the ’cdid’ parameter in the corresponding response before forwarding the response to the DOTS client.

5.2. Unregistering DOTS Clients

A DOTS client de-registers from its DOTS server(s) by deleting the ’cuid’ resource(s). Resources bound to this DOTS client will be deleted by the DOTS server. An example of a de-register request is shown in Figure 15.

DELETE /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=dz6pHjaADkaFTbjr0JGBpw HTTP/1.1 Host: example.com

Figure 15: De-register a DOTS Client

6. Managing DOTS Aliases

The following sub-sections define means for a DOTS client to create aliases (Section 6.1), retrieve one or a list of aliases (Section 6.2), and delete an alias (Section 6.3).



6.1. Create Aliases

A POST or PUT request is used by a DOTS client to create aliases, for resources for which a mitigation may be requested. Such aliases may be used in subsequent DOTS signal channel exchanges to refer more efficiently to the resources under attack.

DOTS clients within the same domain can create different aliases for the same resource.

The structure of POST requests used to create aliases is shown in Figure 16.

POST /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=cuid HTTP/1.1 Host: {host}:{port} Content-Type: application/yang-data+json

{ "ietf-dots-data-channel:aliases": { "alias": [ { "name": "string", "target-prefix": [ "string" ], "target-port-range": [ { "lower-port": integer, "upper-port": integer } ], "target-protocol": [ integer ], "target-fqdn": [ "string" ], "target-uri": [ "string" ] } ] } }

Figure 16: POST to Create Aliases (Request Schema)



The parameters are described below:

name: Name of the alias.


target-prefix: Prefixes are separated by commas. Prefixes are represented using Classless Inter-domain Routing (CIDR) notation [RFC4632]. As a reminder, the prefix length must be less than or equal to 32 (resp. 128) for IPv4 (resp. IPv6).

The prefix list MUST NOT include broadcast, loopback, or multicast addresses. These addresses are considered as invalid values. In addition, the DOTS server MUST validate that these prefixes are within the scope of the DOTS client domain. Other validation checks may be supported by DOTS servers.


target-port-range: A range of port numbers.

The port range is defined by two bounds, a lower port number (lower-port) and an upper port number (upper-port). The range is considered to include both the lower and upper bounds.

When only ’lower-port’ is present, it represents a single port number.

For TCP, UDP, Stream Control Transmission Protocol (SCTP) [RFC4960], or Datagram Congestion Control Protocol (DCCP) [RFC4340], the range of port numbers can be, for example, 1024-65535.


target-protocol: A list of protocols. Values are taken from the IANA protocol registry [proto_numbers].

If ’target-protocol’ is not specified, then the request applies to any protocol.


target-fqdn: A list of Fully Qualified Domain Names (FQDNs) identifying resources under attack [RFC8499].

How a name is passed to an underlying name resolution library is implementation- and deployment-specific. Nevertheless, once the



name is resolved into one or multiple IP addresses, DOTS servers MUST apply the same validation checks as those for ’target- prefix’.

The use of FQDNs may be suboptimal because it does not guarantee that the DOTS server will resolve a name to the same IP addresses that the DOTS client does.


target-uri: A list of Uniform Resource Identifiers (URIs) [RFC3986].

The same validation checks used for ’target-fqdn’ MUST be followed by DOTS servers to validate a target URI.


In POST or PUT requests, at least one of the ’target-prefix’, ’target-fqdn’, or ’target-uri’ attributes MUST be present. DOTS agents can safely ignore Vendor-Specific parameters they don’t understand.

If more than one ’target-*’ scope types (e.g., ’target-prefix’ and ’target-fqdn’ or ’target-fqdn’ and ’target-uri’) are included in a POST or PUT request, the DOTS server binds all resulting IP addresses/prefixes to the same resource.

Figure 17 shows a POST request to create an alias called "https1" for HTTPS servers with IP addresses 2001:db8:6401::1 and 2001:db8:6401::2 listening on TCP port number 443.



POST /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=dz6pHjaADkaFTbjr0JGBpw HTTP/1.1 Host: www.example.com Content-Type: application/yang-data+json

{ "ietf-dots-data-channel:aliases": { "alias": [ { "name": "https1", "target-protocol": [ 6 ], "target-prefix": [ "2001:db8:6401::1/128", "2001:db8:6401::2/128" ], "target-port-range": [ { "lower-port": 443 } ] } ] } }

Figure 17: Example of a POST to Create an Alias

"201 Created" status-line MUST be returned in the response if the DOTS server has accepted the alias.

"409 Conflict" status-line MUST be returned to the requesting DOTS client, if the request is conflicting with an existing alias name. The error-tag "resource-denied" is used in this case.

If the request is missing a mandatory attribute or it contains an invalid or unknown parameter, "400 Bad Request" status-line MUST be returned by the DOTS server. The error-tag is set to "missing- attribute", "invalid-value", or "unknown-element" as a function of the encountered error.

If the request is received via a server-domain DOTS gateway, but the DOTS server does not maintain a ’cdid’ for this ’cuid’ while a ’cdid’ is expected to be supplied, the DOTS server MUST reply with "403 Forbidden" status-line and the error-tag "access-denied". Upon receipt of this message, the DOTS client MUST register (Section 5).



A DOTS client uses the PUT request to modify the aliases in the DOTS server. In particular, a DOTS client MUST update its alias entries upon change of the prefix indicated in the ’target-prefix’.

A DOTS server MUST maintain an alias for at least 10080 minutes (1 week). If no refresh request is seen from the DOTS client, the DOTS server removes expired entries.

6.2. Retrieve Installed Aliases

A GET request is used to retrieve one or all installed aliases by a DOTS client from a DOTS server (Section 3.3.1 in [RFC8040]). If no ’name’ is included in the request, this is an indication that the request is about retrieving all aliases instantiated by the DOTS client.

Figure 18 shows an example to retrieve all the aliases that were instantiated by the requesting DOTS client. The "content" query parameter and its permitted values are defined in Section 4.8.1 of [RFC8040].

GET /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=dz6pHjaADkaFTbjr0JGBpw\ /aliases?content=all HTTP/1.1 Host: example.com Accept: application/yang-data+json

Figure 18: GET to Retrieve All Installed Aliases

Figure 19 shows an example of the response message body that includes all the aliases that are maintained by the DOTS server for the DOTS client identified by the ’cuid’ parameter.



{ "ietf-dots-data-channel:aliases": { "alias": [ { "name": "Server1", "target-protocol": [ 6 ], "target-prefix": [ "2001:db8:6401::1/128", "2001:db8:6401::2/128" ], "target-port-range": [ { "lower-port": 443 } ], "pending-lifetime": 3596 }, { "name": "Server2", "target-protocol": [ 6 ], "target-prefix": [ "2001:db8:6401::10/128", "2001:db8:6401::20/128" ], "target-port-range": [ { "lower-port": 80 } ], "pending-lifetime": 9869 } ] } }

Figure 19: An Example of Response Body Listing All Installed Aliases

Figure 20 shows an example of a GET request to retrieve the alias "Server2" that was instantiated by the DOTS client.



GET /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=dz6pHjaADkaFTbjr0JGBpw\ /aliases/alias=Server2?content=all HTTP/1.1 Host: example.com Accept: application/yang-data+json

Figure 20: GET to Retrieve an Alias

If an alias name (’name’) is included in the request, but the DOTS server does not find that alias name for this DOTS client in its configuration data, it MUST respond with a "404 Not Found" status- line.

6.3. Delete Aliases

A DELETE request is used to delete an alias maintained by a DOTS server.

If the DOTS server does not find the alias name, conveyed in the DELETE request, in its configuration data for this DOTS client, it MUST respond with a "404 Not Found" status-line.

The DOTS server successfully acknowledges a DOTS client’s request to remove the alias using "204 No Content" status-line in the response.

Figure 21 shows an example of a request to delete an alias.

DELETE /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=dz6pHjaADkaFTbjr0JGBpw\ /aliases/alias=Server1 HTTP/1.1 Host: example.com

Figure 21: Delete an Alias

7. Managing DOTS Filtering Rules

The following sub-sections define means for a DOTS client to retrieve DOTS filtering capabilities (Section 7.1), create filtering rules (Section 7.2), retrieve active filtering rules (Section 7.3), and delete a filtering rule (Section 7.4).

7.1. Retrieve DOTS Filtering Capabilities

A DOTS client MAY send a GET request to retrieve the filtering capabilities supported by a DOTS server. Figure 22 shows an example of such request.



GET /restconf/data/ietf-dots-data-channel:dots-data\ /capabilities HTTP/1.1 Host: example.com Accept: application/yang-data+json

Figure 22: GET to Retrieve the Capabilities of a DOTS Server

A DOTS client which issued a GET request to retrieve the filtering capabilities supported by its DOTS server, SHOULD NOT request for filtering actions that are not supported by that DOTS server.

Figure 23 shows an example of a response body received from a DOTS server which supports:

o IPv4, IPv6, TCP, UDP, ICMP, and ICMPv6 mandatory match criteria listed in Section 4.2.

o ’accept’, ’drop’, and ’rate-limit’ actions.



{ "ietf-dots-data-channel:capabilities": { "address-family": ["ipv4", "ipv6"], "forwarding-actions": ["drop", "accept"], "rate-limit": true, "transport-protocols": [1, 6, 17, 58], "ipv4": { "length": true, "protocol": true, "destination-prefix": true, "source-prefix": true, "fragment": true }, "ipv6": { "length": true, "protocol": true, "destination-prefix": true, "source-prefix": true, "fragment": true }, "tcp": { "flags-bitmask": true, "source-port": true, "destination-port": true, "port-range": true }, "udp": { "length": true, "source-port": true, "destination-port": true, "port-range": true }, "icmp": { "type": true, "code": true } } }

Figure 23: Reply to a GET Request with Filtering Capabilities (Message Body)

7.2. Install Filtering Rules

A POST or PUT request is used by a DOTS client to communicate filtering rules to a DOTS server.



Figure 24 shows a POST request example to block traffic from 192.0.2.0/24 and destined to 198.51.100.0/24. Other examples are discussed in Appendix A.

POST /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=dz6pHjaADkaFTbjr0JGBpw HTTP/1.1 Host: example.com Content-Type: application/yang-data+json

{ "ietf-dots-data-channel:acls": { "acl": [ { "name": "sample-ipv4-acl", "type": "ipv4-acl-type", "activation-type": "activate-when-mitigating", "aces": { "ace": [ { "name": "rule1", "matches": { "ipv4": { "destination-ipv4-network": "198.51.100.0/24", "source-ipv4-network": "192.0.2.0/24" } }, "actions": { "forwarding": "drop" } } ] } } ] } }

Figure 24: POST to Install Filtering Rules

The meaning of these parameters is as follows:

name: The name of the access list.


type: Indicates the primary intended type of match criteria (e.g., IPv4, IPv6). It is set to ’ipv4-acl-type’ in the example of Figure 24.




activation-type: Indicates whether an ACL has to be activated (immediately or during mitigation time) or instantiated without being activated (deactivated). Deactivated ACLs can be activated using a variety of means such as manual configuration on a DOTS server or using the DOTS data channel.

If this attribute is not provided, the DOTS server MUST use ’activate-when-mitigating’ as default value.

When a mitigation is in progress, the DOTS server MUST only activate ’activate-when-mitigating’ filters that are bound to the DOTS client that triggered the mitigation.


matches: Define criteria used to identify a flow on which to apply the rule. It can be "l3" (IPv4, IPv6) or "l4" (TCP, UDP, ..). The detailed match parameters are specified in Section 4.

In the example depicted in Figure 24, an IPv4 matching criteria is used.


destination-ipv4-network: The destination IPv4 prefix. DOTS servers MUST validate that these prefixes are within the scope of the DOTS client domain. Other validation checks may be supported by DOTS servers. If this attribute is not provided, the DOTS server enforces the ACL on any destination IP address that belong to the DOTS client domain.

This is a mandatory attribute in requests with an ’activation- type’ set to ’immediate’.

source-ipv4-network: The source IPv4 prefix.


actions: Actions in the forwarding ACL category can be "drop" or "accept". The "accept" action is used to accept-list traffic. The "drop" action is used to drop-list traffic.

Accepted traffic may be subject to "rate-limit"; the allowed traffic rate is represented in bytes per second. This unit is the same as the one used for "traffic-rate" in [RFC5575].




The DOTS server indicates the result of processing the POST request using the status-line. Concretely, "201 Created" status-line MUST be returned in the response if the DOTS server has accepted the filtering rules. If the request is missing a mandatory attribute or contains an invalid or unknown parameter (e.g., a match field not supported by the DOTS server), "400 Bad Request" status-line MUST be returned by the DOTS server in the response. The error-tag is set to "missing-attribute", "invalid-value", or "unknown-element" as a function of the encountered error.

If the request is received via a server-domain DOTS gateway, but the DOTS server does not maintain a ’cdid’ for this ’cuid’ while a ’cdid’ is expected to be supplied, the DOTS server MUST reply with "403 Forbidden" status-line and the error-tag "access-denied". Upon receipt of this message, the DOTS client MUST register (Figure 11).

If the request is conflicting with an existing filtering installed by another DOTS client of the domain, absent any local policy, the DOTS server returns "409 Conflict" status-line to the requesting DOTS client. The error-tag "resource-denied" is used in this case.

The "insert" query parameter (Section 4.8.5 of [RFC8040]) MAY be used to specify how an access control entry is inserted within an ACL and how an ACL is inserted within an ACL set.

The DOTS client uses the PUT request to modify its filtering rules maintained by the DOTS server. In particular, a DOTS client MUST update its filtering entries upon change of the destination-prefix. How such change is detected is out of scope.

A DOTS server MUST maintain a filtering rule for at least 10080 minutes (1 week). If no refresh request is seen from the DOTS client, the DOTS server removes expired entries. Typically, a refresh request is a PUT request which echoes the content of a response to a GET request with all of the read-only parameters stripped out (e.g., pending-lifetime).

7.3. Retrieve Installed Filtering Rules

A DOTS client periodically queries its DOTS server to check the counters for installed filtering rules. A GET request is used to retrieve filtering rules from a DOTS server. In order to indicate which type of data is requested in a GET request, the DOTS client sets adequately the "content" query parameter.



If the DOTS server does not find the access list name conveyed in the GET request in its configuration data for this DOTS client, it responds with a "404 Not Found" status-line.

In order to illustrate the intended behavior, consider the example depicted in Figure 25. In reference to this example, the DOTS client requests the creation of an immediate ACL called "test-acl-ipv6-udp".



PUT /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=paL8p4Zqo4SLv64TLPXrxA/acls\ /acl=test-acl-ipv6-udp HTTP/1.1 Host: example.com Content-Type: application/yang-data+json

{ "ietf-dots-data-channel:acls": { "acl": [ { "name": "test-acl-ipv6-udp", "type": "ipv6-acl-type", "activation-type": "immediate", "aces": { "ace": [ { "name": "my-test-ace", "matches": { "ipv6": { "destination-ipv6-network": "2001:db8:6401::2/127", "source-ipv6-network": "2001:db8:1234::/96", "protocol": 17, "flow-label": 10000 }, "udp": { "source-port": { "operator": "lte", "port": 80 }, "destination-port": { "operator": "neq", "port": 1010 } } }, "actions": { "forwarding": "accept" } } ] } } ] } }

Figure 25: Example of a PUT Request to Create a Filtering



The peer DOTS server follows the procedure specified in Section 7.2 to process the request. We consider in the following that a positive response is sent back to the requesting DOTS client to confirm that the "test-acl-ipv6-udp" ACL is successfully installed by the DOTS server.

The DOTS client can issue a GET request to retrieve all its filtering rules and the number of matches for the installed filtering rules as illustrated in Figure 26. The "content" query parameter is set to ’all’. The message body of the response to this GET request is shown in Figure 27.

GET /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=dz6pHjaADkaFTbjr0JGBpw\ /acls?content=all HTTP/1.1 Host: example.com Accept: application/yang-data+json

Figure 26: Retrieve the Configuration Data and State Data for the Filtering Rules (GET Request)



{ "ietf-dots-data-channel:acls": { "acl": [ { "name": "test-acl-ipv6-udp", "type": "ipv6-acl-type", "activation-type": "immediate", "pending-lifetime":9080, "aces": { "ace": [ { "name": "my-test-ace", "matches": { "ipv6": { "destination-ipv6-network": "2001:db8:6401::2/127", "source-ipv6-network": "2001:db8:1234::/96", "protocol": 17, "flow-label": 10000 }, "udp": { "source-port": { "operator": "lte", "port": 80 }, "destination-port": { "operator": "neq", "port": 1010 } } }, "actions": { "forwarding": "accept" } } ] } } ] } }

Figure 27: Retrieve the Configuration Data and State Data for the Filtering Rules (Response Message Body)

Also, a DOTS client can issue a GET request to retrieve only configuration data related to an ACL as shown in Figure 28. It does so by setting the "content" query parameter to ’config’.



GET /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=paL8p4Zqo4SLv64TLPXrxA/acls\ /acl=test-acl-ipv6-udp?content=config HTTP/1.1 Host: example.com Accept: application/yang-data+json

Figure 28: Retrieve the Configuration Data for a Filtering Rule (GET Request)

A response to this GET request is shown in Figure 29.



{ "ietf-dots-data-channel:acls": { "acl": [ { "name": "test-acl-ipv6-udp", "type": "ipv6-acl-type", "activation-type": "immediate", "aces": { "ace": [ { "name": "my-test-ace", "matches": { "ipv6": { "destination-ipv6-network": "2001:db8:6401::2/127", "source-ipv6-network": "2001:db8:1234::/96", "protocol": 17, "flow-label": 10000 }, "udp": { "source-port": { "operator": "lte", "port": 80 }, "destination-port": { "operator": "neq", "port": 1010 } } }, "actions": { "forwarding": "accept" } } ] } } ] } }

Figure 29: Retrieve the Configuration Data for a Filtering Rule (Response Message Body)

A DOTS client can also issue a GET request with a "content" query parameter set to ’non-config’ to exclusively retrieve non- configuration data bound to a given ACL as shown in Figure 30. A response to this GET request is shown in Figure 31.



GET /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=paL8p4Zqo4SLv64TLPXrxA/acls\ /acl=test-acl-ipv6-udp?content=non-config HTTP/1.1 Host: example.com Accept: application/yang-data+json

Figure 30: Retrieve the Non-Configuration Data for a Filtering Rule (GET Request)

{ "ietf-dots-data-channel:acls": { "acl": [ { "name": "test-acl-ipv6-udp", "pending-lifetime": 8000, "aces": { "ace": [ { "name": "my-test-ace" } ] } } ] } }

Figure 31: Retrieve the Non-Configuration Data for a Filtering Rule (Response Message Body)

7.4. Remove Filtering Rules

A DELETE request is used by a DOTS client to delete filtering rules from a DOTS server.

If the DOTS server does not find the access list name carried in the DELETE request in its configuration data for this DOTS client, it MUST respond with a "404 Not Found" status-line. The DOTS server successfully acknowledges a DOTS client’s request to withdraw the filtering rules using "204 No Content" status-line, and removes the filtering rules accordingly.

Figure 32 shows an example of a request to remove the IPv4 ACL "sample-ipv4-acl" created in Section 7.2.



DELETE /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=dz6pHjaADkaFTbjr0JGBpw/acls\ /acl=sample-ipv4-acl HTTP/1.1 Host: example.com

Figure 32: Remove a Filtering Rule (DELETE Request)

Figure 33 shows an example of a response received from the DOTS server to confirm the deletion of "sample-ipv4-acl".

HTTP/1.1 204 No Content Server: Apache Date: Fri, 27 Jul 2018 10:05:15 GMT Cache-Control: no-cache Content-Type: application/yang-data+json Content-Length: 0 Connection: Keep-Alive

Figure 33: Remove a Filtering Rule (Response)

8. Operational Considerations

The following operational considerations should be taken into account:

o DOTS servers MUST NOT enable both DOTS data channel and direct configuration, to avoid race conditions and inconsistent configurations arising from simultaneous updates from multiple sources.

o DOTS agents SHOULD enable the DOTS data channel to configure aliases and ACLs, and only use direct configuration as a stop-gap mechanism to test DOTS signal channel with aliases and ACLs. Further, direct configuration SHOULD only be used when the on-path DOTS agents are within the same domain.

o If a DOTS server has enabled direct configuration, it can reject the DOTS data channel connection using hard ICMP error [RFC1122] or RST (Reset) bit in the TCP header or reject the RESTCONF request using an error response containing a "503 Service Unavailable" status-line.


This document requests IANA to register the following URI in the "ns" subregistry within the "IETF XML Registry" [RFC3688]:



URI: urn:ietf:params:xml:ns:yang:ietf-dots-data-channel Registrant Contact: The IESG. XML: N/A; the requested URI is an XML namespace.

This document requests IANA to register the following YANG module in the "YANG Module Names" subregistry [RFC7950] within the "YANG Parameters" registry.

Name: ietf-dots-data-channel Namespace: urn:ietf:params:xml:ns:yang:ietf-dots-data-channel Prefix: data-channel Reference: RFC XXXX

This module is not maintained by IANA.


RESTCONF security considerations are discussed in [RFC8040]. In particular, DOTS agents MUST follow the security recommendations in Sections 2 and 12 of [RFC8040]. Also, DOTS agents MUST support the mutual authentication TLS profile discussed in Sections 7.1 and 8 of [I-D.ietf-dots-signal-channel].

Authenticated encryption MUST be used for data confidentiality and message integrity. The interaction between the DOTS agents requires Transport Layer Security (TLS) with a cipher suite offering confidentiality protection and the guidance given in [RFC7525] MUST be followed to avoid attacks on TLS.

The installation of drop- or accept-list rules using RESTCONF over TLS reveals the attacker IP addresses and legitimate IP addresses only to the DOTS server trusted by the DOTS client. The secure communication channel between DOTS agents provides privacy and prevents a network eavesdropper from directly gaining access to the drop- and accept-listed IP addresses.

An attacker may be able to inject RST packets, bogus application segments, etc., regardless of whether TLS authentication is used. Because the application data is TLS protected, this will not result in the application receiving bogus data, but it will constitute a DoS on the connection. This attack can be countered by using TCP-AO [RFC5925]. If TCP-AO is used, then any bogus packets injected by an attacker will be rejected by the TCP-AO integrity check and therefore will never reach the TLS layer.

In order to prevent leaking internal information outside a client- domain, client-side DOTS gateways SHOULD NOT reveal the identity of



internal DOTS clients (e.g., source IP address, client’s hostname) unless explicitly configured to do so.

DOTS servers MUST verify that requesting DOTS clients are entitled to enforce filtering rules on a given IP prefix. That is, only filtering rules on IP resources that belong to the DOTS client domain can be authorized by a DOTS server. The exact mechanism for the DOTS servers to validate that the target prefixes are within the scope of the DOTS client domain is deployment-specific.

Rate-limiting DOTS requests, including those with new ’cuid’ values, from the same DOTS client defends against DoS attacks that would result from varying the ’cuid’ to exhaust DOTS server resources. Rate-limit policies SHOULD be enforced on DOTS gateways (if deployed) and DOTS servers.

Applying resources quota per DOTS client and/or per DOTS client domain (e.g., limit the number of aliases and filters to be installed by DOTS clients) prevents DOTS server resources to be aggressively used by some DOTS clients and ensures, therefore, DDoS mitigation usage fairness. Additionally, DOTS servers may limit the number of DOTS clients that can be enabled per domain.

When FQDNs are used as targets, the DOTS server MUST rely upon DNS privacy enabling protocols (e.g., DNS over TLS [RFC7858] or DoH [RFC8484]) to prevent eavesdroppers from possibly identifying the target resources protected by the DDoS mitigation service, and means to ensure the target FQDN resolution is authentic (e.g., DNSSEC [RFC4034]).

The presence of DOTS gateways may lead to infinite forwarding loops, which is undesirable. To prevent and detect such loops, a mechanism is defined in Section 3.4.

All data nodes defined in the YANG module which can be created, modified, and deleted (i.e., config true, which is the default) are considered sensitive. Write operations applied to these data nodes without proper protection can negatively affect network operations. This module reuses YANG structures from [RFC8519], and the security considerations for those nodes continue to apply for this usage. Appropriate security measures are recommended to prevent illegitimate users from invoking DOTS data channel primitives. Nevertheless, an attacker who can access a DOTS client is technically capable of launching various attacks, such as:

o Setting an arbitrarily low rate-limit, which may prevent legitimate traffic from being forwarded (rate-limit).



o Setting an arbitrarily high rate-limit, which may lead to the forwarding of illegitimate DDoS traffic (rate-limit).

o Communicating invalid aliases to the server (alias), which will cause the failure of associating both data and signal channels.

o Setting invalid ACL entries, which may prevent legitimate traffic from being forwarded. Likewise, invalid ACL entries may lead to forward DDoS traffic.

11. Contributing Authors

The following individuals co-authored this document:





Liang Xia Huawei 101 Software Avenue, Yuhuatai District Nanjing, Jiangsu 210012 China






Nik Teague Iron Mountain Data Centers United Kingdom


12. Contributors


o Dan Wing, Email: [email protected]

o Jon Shallow, NCC Group, Email: [email protected]




Thanks to Christian Jacquenet, Roland Dobbins, Roman Danyliw, Ehud Doron, Russ White, Gilbert Clark, Kathleen Moriarty, Nesredien Suleiman, Roni Even, and Brian Trammel for the discussion and comments.

The authors would like to give special thanks to Kaname Nishizuka and Jon Shallow for their efforts in implementing the protocol and performing interop testing at IETF Hackathons.

Many thanks to Ben Kaduk for the detailed AD review.

Thanks to Martin Bjorklund for the guidance on RESTCONF.

Thanks to Alexey Melnikov, Adam Roach, Suresh Krishnan, Mirja Kuehlewind, and Warren Kumari for the review.

14. References


[I-D.ietf-dots-signal-channel] K, R., Boucadair, M., Patil, P., Mortensen, A., and N. Teague, "Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification", draft- ietf-dots-signal-channel-35 (work in progress), July 2019.


[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, <https://www.rfc-editor.org/info/rfc3688>.

[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 2006, <https://www.rfc-editor.org/info/rfc4632>.




[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, July 2013, <https://www.rfc-editor.org/info/rfc6991>.

[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014, <https://www.rfc-editor.org/info/rfc7230>.

[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, "Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 2015, <https://www.rfc-editor.org/info/rfc7525>.

[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, <https://www.rfc-editor.org/info/rfc7950>.

[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG", RFC 7951, DOI 10.17487/RFC7951, August 2016, <https://www.rfc-editor.org/info/rfc7951>.

[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, <https://www.rfc-editor.org/info/rfc8040>.


[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017, <https://www.rfc-editor.org/info/rfc8259>.

[RFC8519] Jethanandani, M., Agarwal, S., Huang, L., and D. Blair, "YANG Data Model for Network Access Control Lists (ACLs)", RFC 8519, DOI 10.17487/RFC8519, March 2019, <https://www.rfc-editor.org/info/rfc8519>.


[I-D.ietf-dots-architecture] Mortensen, A., K, R., Andreasen, F., Teague, N., and R. Compton, "Distributed-Denial-of-Service Open Threat Signaling (DOTS) Architecture", draft-ietf-dots- architecture-14 (work in progress), May 2019.



[I-D.ietf-dots-server-discovery] Boucadair, M. and R. K, "Distributed-Denial-of-Service Open Threat Signaling (DOTS) Server Discovery", draft- ietf-dots-server-discovery-04 (work in progress), June 2019.

[I-D.ietf-netconf-restconf-client-server] Watsen, K., "RESTCONF Client and Server Models", draft- ietf-netconf-restconf-client-server-14 (work in progress), July 2019.

[proto_numbers] "IANA, "Protocol Numbers"", 2011, <http://www.iana.org/assignments/protocol-numbers>.

[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, DOI 10.17487/RFC1122, October 1989, <https://www.rfc-editor.org/info/rfc1122>.

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, <https://www.rfc-editor.org/info/rfc3986>.

[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Resource Records for the DNS Security Extensions", RFC 4034, DOI 10.17487/RFC4034, March 2005, <https://www.rfc-editor.org/info/rfc4034>.

[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram Congestion Control Protocol (DCCP)", RFC 4340, DOI 10.17487/RFC4340, March 2006, <https://www.rfc-editor.org/info/rfc4340>.

[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol", RFC 4960, DOI 10.17487/RFC4960, September 2007, <https://www.rfc-editor.org/info/rfc4960>.

[RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J., and D. McPherson, "Dissemination of Flow Specification Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009, <https://www.rfc-editor.org/info/rfc5575>.

[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP Authentication Option", RFC 5925, DOI 10.17487/RFC5925, June 2010, <https://www.rfc-editor.org/info/rfc5925>.



[RFC6520] Seggelmann, R., Tuexen, M., and M. Williams, "Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) Heartbeat Extension", RFC 6520, DOI 10.17487/RFC6520, February 2012, <https://www.rfc-editor.org/info/rfc6520>.

[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., and P. Hoffman, "Specification for DNS over Transport Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 2016, <https://www.rfc-editor.org/info/rfc7858>.

[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, <https://www.rfc-editor.org/info/rfc8340>.

[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, <https://www.rfc-editor.org/info/rfc8484>.

[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499, January 2019, <https://www.rfc-editor.org/info/rfc8499>.


Appendix A. Sample Examples: Filtering Fragments

This specification strongly recommends the use of "fragment" for handling fragments.

Figure 34 shows the content of the POST request to be issued by a DOTS client to its DOTS server to allow the traffic destined to 198.51.100.0/24 and UDP port number 53, but to drop all fragmented packets. The following ACEs are defined (in this order):

o "drop-all-fragments" ACE: discards all fragments.

o "allow-dns-packets" ACE: accepts DNS packets destined to 198.51.100.0/24.




{ "ietf-dots-data-channel:acls": { "acl": [ { "name": "dns-fragments", "type": "ipv4-acl-type", "aces": { "ace": [ { "name": "drop-all-fragments", "matches": { "ipv4": { "fragment": { "operator": "match", "type": "isf" } } }, "actions": { "forwarding": "drop" } } ] "ace": [ { "name": "allow-dns-packets", "matches": { "ipv4": { "destination-ipv4-network": "198.51.100.0/24" } "udp": { "destination-port": { "operator": "eq", "port": 53 } }, "actions": { "forwarding": "accept" } } ] } } ] } }

Figure 34: Filtering IPv4 Fragmented Packets



Figure 35 shows a POST request example issued by a DOTS client to its DOTS server to allow the traffic destined to 2001:db8::/32 and UDP port number 53, but to drop all fragmented packets. The following ACEs are defined (in this order):

o "drop-all-fragments" ACE: discards all fragments (including atomic fragments). That is, IPv6 packets which include a Fragment header (44) are dropped.

o "allow-dns-packets" ACE: accepts DNS packets destined to 2001:db8::/32.


{ "ietf-dots-data-channel:acls": { "acl": [ { "name": "dns-fragments", "type": "ipv6-acl-type", "aces": { "ace": [ { "name": "drop-all-fragments", "matches": { "ipv6": { "fragment": { "operator": "match", "type": "isf" } } }, "actions": { "forwarding": "drop" } } ] "ace": [ { "name": "allow-dns-packets", "matches": { "ipv6": { "destination-ipv6-network": "2001:db8::/32" } "udp": {



"destination-port": { "operator": "eq", "port": 53 } } }, "actions": { "forwarding": "accept" } } ] } } ] } }

Figure 35: Filtering IPv6 Fragmented Packets

Appendix B. Sample Examples: Filtering TCP Messages

This section provides sample examples to illustrate TCP-specific filtering based on the flag bits. These examples should not be interpreted as recommended filtering behaviors under specific DDoS attacks.

B.1. Discard TCP Null Attack

Figure 36 shows an example of a DOTS request sent by a DOTS client to install immediately a filter to discard incoming TCP messages having all flags unset. The bitmask can be set to 255 to check against the (CWR, ECE, URG, ACK, PSH, RST, SYN, FIN) flags.



PUT /restconf/data/ietf-dots-data-channel:dots-data\ /dots-client=paL8p4Zqo4SLv64TLPXrxA/acls\ /acl=tcp-flags-example HTTP/1.1 Host: example.com Content-Type: application/yang-data+json

{ "ietf-dots-data-channel:acls": { "acl": [{ "name": "tcp-flags-example", "activation-type": "immediate", "aces": { "ace": [{ "name": "null-attack", "matches": { "tcp": { "flags-bitmask": { "operator": "not any", "bitmask": 4095 } } }, "actions": { "forwarding": "drop" } }] } }] } }

Figure 36: Example of a DOTS Request to Deny TCP Null Attack Messages

B.2. Rate-Limit SYN Flooding

Figure 37 shows an ACL example to rate-limit incoming SYNs during a SYN-flood attack.




{ "ietf-dots-data-channel:acls": { "acl": [{ "name": "tcp-flags-example", "activation-type": "activate-when-mitigating", "aces": { "ace": [{ "name": "rate-limit-syn", "matches": { "tcp": { "flags-bitmask": { "operator": "match", "bitmask": 2 } } }, "actions": { "forwarding": "accept", "rate-limit": "20.00" } }] } }] } }

Figure 37: Example of DOTS Request to Rate-Limit Incoming TCP SYNs

B.3. Rate-Limit ACK Flooding

Figure 38 shows an ACL example to rate-limit incoming ACKs during an ACK-flood attack.




{ "ietf-dots-data-channel:acls": { "acl": [{ "name": "tcp-flags-example", "type": "ipv4-acl-type", "activation-type": "activate-when-mitigating", "aces": { "ace": [{ "name": "rate-limit-ack", "matches": { "tcp": { "flags-bitmask": { "operator": "match", "bitmask": 16 } } }, "actions": { "forwarding": "accept", "rate-limit": "20.00" } }] } }] } }

Figure 38: Example of DOTS Request to Rate-Limit Incoming TCP ACKs


Mohamed Boucadair (editor) Orange Rennes 35000 France



DOTS A. MortensenInternet-Draft Arbor NetworksIntended status: Informational R. MoskowitzExpires: January 4, 2018 HTT Consulting T. Reddy McAfee, Inc. July 03, 2017

Distributed Denial of Service (DDoS) Open Threat Signaling Requirements draft-ietf-dots-requirements-06

Abstract

This document defines the requirements for the Distributed Denial of Service (DDoS) Open Threat Signaling (DOTS) protocols coordinating attack response against DDoS attacks.

Status of This Memo





Copyright Notice


This document is subject to BCP 78 and the IETF Trust’s Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of


Internet-Draft DOTS Requirements July 2017

the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Context and Motivation . . . . . . . . . . . . . . . . . 2 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. General Requirements . . . . . . . . . . . . . . . . . . 7 2.2. Signal Channel Requirements . . . . . . . . . . . . . . . 7 2.3. Data Channel Requirements . . . . . . . . . . . . . . . . 11 2.4. Security requirements . . . . . . . . . . . . . . . . . . 13 2.5. Data Model Requirements . . . . . . . . . . . . . . . . . 14 3. Congestion Control Considerations . . . . . . . . . . . . . . 15 3.1. Signal Channel . . . . . . . . . . . . . . . . . . . . . 15 3.2. Data Channel . . . . . . . . . . . . . . . . . . . . . . 15 4. Security Considerations . . . . . . . . . . . . . . . . . . . 15 5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 16 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 7. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 16 7.1. 04 revision . . . . . . . . . . . . . . . . . . . . . . . 16 7.2. 03 revision . . . . . . . . . . . . . . . . . . . . . . . 17 7.3. 02 revision . . . . . . . . . . . . . . . . . . . . . . . 17 7.4. 01 revision . . . . . . . . . . . . . . . . . . . . . . . 17 7.5. 00 revision . . . . . . . . . . . . . . . . . . . . . . . 18 7.6. Initial revision . . . . . . . . . . . . . . . . . . . . 18 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 8.1. Normative References . . . . . . . . . . . . . . . . . . 18 8.2. Informative References . . . . . . . . . . . . . . . . . 19 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 20

1. Introduction

1.1. Context and Motivation

Distributed Denial of Service (DDoS) attacks continue to plague network operators around the globe, from Tier-1 service providers on down to enterprises and small businesses. Attack scale and frequency similarly have continued to increase, in part as a result of software vulnerabilities leading to reflection and amplification attacks. Once-staggering attack traffic volume is now the norm, and the impact of larger-scale attacks attract the attention of international press agencies.

The greater impact of contemporary DDoS attacks has led to increased focus on coordinated attack response. Many institutions and enterprises lack the resources or expertise to operate on-premises



attack mitigation solutions themselves, or simply find themselves constrained by local bandwidth limitations. To address such gaps, security service providers have begun to offer on-demand traffic scrubbing services, which aim to separate the DDoS traffic from legitimate traffic and forward only the latter. Today each such service offers its own interface for subscribers to request attack mitigation, tying subscribers to proprietary signaling implementations while also limiting the subset of network elements capable of participating in the attack response. As a result of signaling interface incompatibility, attack responses may be fragmentary or otherwise incomplete, leaving key players in the attack path unable to assist in the defense.

The lack of a common method to coordinate a real-time response among involved actors and network domains inhibits the speed and effectiveness of DDoS attack mitigation. This document describes the required characteristics of a protocol enabling requests for DDoS attack mitigation, reducing attack impact and leading to more efficient defensive strategies.

DOTS communicates the need for defensive action in anticipation of or in response to an attack, but does not dictate the form any defensive action takes. DOTS supplements calls for help with pertinent details about the detected attack, allowing entities participating in DOTS to form ad hoc, adaptive alliances against DDoS attacks as described in the DOTS use cases [I-D.ietf-dots-use-cases]. The requirements in this document are derived from those use cases and [I-D.ietf-dots-architecture].

1.2. Terminology


This document adopts the following terms:

DDoS: A distributed denial-of-service attack, in which traffic originating from multiple sources are directed at a target on a network. DDoS attacks are intended to cause a negative impact on the availability of servers, services, applications, and/or other functionality of an attack target. Denial-of-service considerations are discussed in detail in [RFC4732].

DDoS attack target: A network connected entity with a finite set of resources, such as network bandwidth, memory or CPU, that is the focus of a DDoS attack. Potential targets include network elements, network links, servers, and services.



DDoS attack telemetry: Collected measurements and behavioral characteristics defining the nature of a DDoS attack.

Countermeasure: An action or set of actions taken to recognize and filter out DDoS attack traffic while passing legitimate traffic to the attack target.

Mitigation: A set of countermeasures enforced against traffic destined for the target or targets of a detected or reported DDoS attack, where countermeasure enforcement is managed by an entity in the network path between attack sources and the attack target. Mitigation methodology is out of scope for this document.

Mitigator: An entity, typically a network element, capable of performing mitigation of a detected or reported DDoS attack. For the purposes of this document, this entity is a black box capable of mitigation, making no assumptions about availability or design of countermeasures, nor about the programmable interface between this entity and other network elements. The mitigator and DOTS server are assumed to belong to the same administrative entity.

DOTS client: A DOTS-aware software module responsible for requesting attack response coordination with other DOTS-aware elements.

DOTS server: A DOTS-aware software module handling and responding to messages from DOTS clients. The DOTS server SHOULD enable mitigation on behalf of the DOTS client, if requested, by communicating the DOTS client’s request to the mitigator and returning selected mitigator feedback to the requesting DOTS client. A DOTS server MAY also be a mitigator.

DOTS agent: Any DOTS-aware software module capable of participating in a DOTS signal or data channel.

DOTS gateway: A logical DOTS agent resulting from the logical concatenation of a DOTS server and a DOTS client, analogous to a SIP Back-to-Back User Agent (B2BUA) [RFC3261]. DOTS gateways are discussed in detail in [I-D.ietf-dots-architecture].

Signal channel: A bidirectional, mutually authenticated communication channel between DOTS agents characterized by resilience even in conditions leading to severe packet loss, such as a volumetric DDoS attack causing network congestion.

DOTS signal: A concise authenticated status/control message transmitted between DOTS agents, used to indicate client’s need for mitigation, as well as to convey the status of any requested mitigation.



Heartbeat: A message transmitted between DOTS agents over the signal channel, used as a keep-alive and to measure peer health.

Client signal: A message sent from a DOTS client to a DOTS server over the signal channel, indicating the DOTS client’s need for mitigation, as well as the scope of any requested mitigation, optionally including additional attack details to supplement server-initiated mitigation.

Server signal: A message sent from a DOTS server to a DOTS client over the signal channel. Note that a server signal is not a response to client signal, but a DOTS server-initiated status message sent to DOTS clients with which the server has established signal channels.

Data channel: A secure communication layer between DOTS clients and DOTS servers used for infrequent bulk exchange of data not easily or appropriately communicated through the signal channel under attack conditions.

Filter: A policy matching a network traffic flow or set of flows and rate-limiting or discarding matching traffic.

Blacklist: A filter list of addresses, prefixes and/or other identifiers indicating sources from which traffic should be blocked, regardless of traffic content.

Whitelist: A list of addresses, prefixes and/or other identifiers from indicating sources from which traffic should always be allowed, regardless of contradictory data gleaned in a detected attack.

Multi-homed DOTS client: A DOTS client exchanging messages with multiple DOTS servers, each in a separate administrative domain.

2. Requirements

This section describes the required features and characteristics of the DOTS protocol.

DOTS is an advisory protocol. An active DDoS attack against the entity controlling the DOTS client need not be present before establishing a communication channel between DOTS agents. Indeed, establishing a relationship with peer DOTS agents during normal network conditions provides the foundation for more rapid attack response against future attacks, as all interactions setting up DOTS, including any business or service level agreements, are already complete.



The DOTS protocol must at a minimum make it possible for a DOTS client to request a mitigator’s aid mounting a defense, coordinated by a DOTS server, against a suspected attack, signaling within or between domains as requested by local operators. DOTS clients should similarly be able to withdraw aid requests. DOTS requires no justification from DOTS clients for requests for help, nor do DOTS clients need to justify withdrawing help requests: the decision is local to the DOTS clients’ domain.

Regular feedback between DOTS clients and DOTS server supplement the defensive alliance by maintaining a common understanding of DOTS agent health and activity. Bidirectional communication between DOTS clients and DOTS servers is therefore critical.

DOTS protocol implementations face competing operational goals when maintaining this bidirectional communication stream. On the one hand, the protocol must be resilient under extremely hostile network conditions, providing continued contact between DOTS agents even as attack traffic saturates the link. Such resiliency may be developed several ways, but characteristics such as small message size, asynchronous, redundant message delivery and minimal connection overhead (when possible given local network policy) will tend to contribute to the robustness demanded by a viable DOTS protocol. Operators of peer DOTS-enabled domains may enable quality- or class- of-service traffic tagging to increase the probability of successful DOTS signal delivery, but DOTS requires no such policies be in place. The DOTS solution indeed must be viable especially in their absence.

On the other hand, DOTS must include protections ensuring message confidentiality, integrity and authenticity to keep the protocol from becoming another vector for the very attacks it’s meant to help fight off. DOTS clients must be able to authenticate DOTS servers, and vice versa, to avoid exposing new attack surfaces when deploying DOTS; specifically, to prevent DDoS mitigation in response to DOTS signaling from becoming a new form of attack. In order to provide this level of proteection, DOTS agents must have a way to negotiate and agree upon the terms of protocol security. Attacks against the transport protocol should not offer a means of attack against the message confidentiality, integrity and authenticity.

The DOTS server and client must also have some common method of defining the scope of any mitigation performed by the mitigator, as well as making adjustments to other commonly configurable features, such as listen ports, exchanging black- and white-lists, and so on.

Finally, DOTS should be sufficiently extensible to meet future needs in coordinated attack defense, although this consideration is necessarily superseded by the other operational requirements.



2.1. General Requirements

GEN-001 Extensibility: Protocols and data models developed as part of DOTS MUST be extensible in order to keep DOTS adaptable to operational and proprietary DDoS defenses. Future extensions MUST be backward compatible. DOTS protocols MUST use a version number system to distinguish protocol revisions. Implementations of older protocol versions SHOULD ignore information added to DOTS messages as part of newer protocol versions.

GEN-002 Resilience and Robustness: The signaling protocol MUST be designed to maximize the probability of signal delivery even under the severely constrained network conditions imposed by particular attack traffic. The protocol MUST be resilient, that is, continue operating despite message loss and out-of-order or redundant message delivery. In support signaling protocol robustness, DOTS signals SHOULD be conveyed over a transport not susceptible to Head of Line Blocking.

GEN-003 Bidirectionality: To support peer health detection, to maintain an open signal channel, and to increase the probability of signal delivery during attack, the signal channel MUST be bidirectional, with client and server transmitting signals to each other at regular intervals, regardless of any client request for mitigation. Unidirectional messages MUST be supported within the bidirectional signal channel to allow for unsolicited message delivery, enabling asynchronous notifications between agents.

GEN-004 Bulk Data Exchange: Infrequent bulk data exchange between DOTS agents can also significantly augment attack response coordination, permitting such tasks as population of black- or white-listed source addresses; address or prefix group aliasing; exchange of incident reports; and other hinting or configuration supplementing attack response.

As the resilience requirements for the DOTS signal channel mandate small signal message size, a separate, secure data channel utilizing a reliable transport protocol MUST be used for bulk data exchange.

2.2. Signal Channel Requirements

SIG-001 Use of Common Transport Protocols: DOTS MUST operate over common widely deployed and standardized transport protocols. While connectionless transport such as the User Datagram Protocol (UDP) [RFC0768] SHOULD be used for the signal channel, the Transmission Control Protocol (TCP) [RFC0793] MAY be used if



necessary due to network policy or middlebox capabilities or configurations.

SIG-002 Sub-MTU Message Size: To avoid message fragmentation and the consequently decreased probability of message delivery over a congested link, signaling protocol message size MUST be kept under signaling Path Maximum Transmission Unit (PMTU), including the byte overhead of any encapsulation, transport headers, and transport- or message-level security.

DOTS agents SHOULD attempt to learn the PMTU through mechanisms such as Path MTU Discovery [RFC1191] or Packetization Layer Path MTU Discovery [RFC4821]. If the PMTU cannot be discovered, DOTS agents SHOULD assume a PMTU of 1280 bytes. If IPv4 support on legacy or otherwise unusual networks is a consideration and PMTU is unknown, DOTS implementations MAY rely on a PMTU of 576 bytes, as discussed in [RFC0791] and [RFC1122].

SIG-003 Channel Health Monitoring: Peer DOTS agents MUST regularly send heartbeats to each other after mutual authentication in order to keep the DOTS signal channel active. A signal channel MUST be considered active until a DOTS agent explicitly ends the session, or either DOTS agent fails to receive heartbeats from the other after a mutually agreed upon timeout period has elapsed.

SIG-004 Channel Redirection: In order to increase DOTS operational flexibility and scalability, DOTS servers SHOULD be able to redirect DOTS clients to another DOTS server at any time. DOTS clients MUST NOT assume the redirection target DOTS server shares security state with the redirecting DOTS server. DOTS clients MAY attempt abbreviated security negotiation methods supported by the protocol, such as DTLS session resumption, but MUST be prepared to negotiate new security state with the redirection target DOTS server.

Due to the increased likelihood of packet loss caused by link congestion during an attack, DOTS servers SHOULD NOT redirect while mitigation is enabled during an active attack against a target in the DOTS client’s domain.

SIG-005 Mitigation Requests and Status: Authorized DOTS clients MUST be able to request scoped mitigation from DOTS servers. DOTS servers MUST send mitigation request status in response to DOTS clients requests for mitigation, and SHOULD accept scoped mitigation requests from authorized DOTS clients. DOTS servers MAY reject authorized requests for mitigation, but MUST include a reason for the rejection in the status message sent to the client.



Due to the higher likelihood of packet loss during a DDoS attack, DOTS servers SHOULD regularly send mitigation status to authorized DOTS clients which have requested and been granted mitigation, regardless of client requests for mitigation status.

When DOTS client-requested mitigation is active, DOTS server status messages SHOULD include the following mitigation metrics:

* Total number of packets blocked by the mitigation

* Current number of packets per second blocked

* Total number of bytes blocked

* Current number of bytes per second blocked

DOTS clients MAY take these metrics into account when determining whether to ask the DOTS server to cease mitigation.

Once a DOTS client requests mitigation, the client MAY withdraw that request at any time, regardless of whether mitigation is currently active. The DOTS server MUST immediately acknowledge a DOTS client’s request to stop mitigation.

To protect against route or DNS flapping caused by a client rapidly toggling mitigation, and to dampen the effect of oscillating attacks, DOTS servers MAY allow mitigation to continue for a limited period after acknowledging a DOTS client’s withdrawal of a mitigation request. During this period, DOTS server status messages SHOULD indicate that mitigation is active but terminating.

The active-but-terminating period is initially 30 seconds. If the client requests mitigation again before that 30 second window elapses, the DOTS server MAY exponentially increase the active- but-terminating period up to a maximum of 240 seconds (4 minutes). After the active-but-terminating period elapses, the DOTS server MUST treat the mitigation as terminated, as the DOTS client is no longer responsible for the mitigation. For example, if there is a financial relationship between the DOTS client and server domains, the DOTS client ceases incurring cost at this point.

SIG-006 Mitigation Lifetime: DOTS servers MUST support mitigation lifetimes, and MUST terminate a mitigation when the lifetime elapses. DOTS servers also MUST support renewal of mitigation lifetimes in mitigation requests from DOTS clients, allowing clients to extend mitigation as necessary for the duration of an attack.



DOTS servers MUST treat a mitigation terminated due to lifetime expiration exactly as if the DOTS client originating the mitigation had asked to end the mitigation, including the active- but-terminating period, as described above in SIG-005.

DOTS clients SHOULD include a mitigation lifetime in all mitigation requests. If a DOTS client does not include a mitigation lifetime in requests for help sent to the DOTS server, the DOTS server will use a reasonable default as defined by the protocol.

DOTS servers SHOULD support indefinite mitigation lifetimes, enabling architectures in which the mitigator is always in the traffic path to the resources for which the DOTS client is requesting protection. DOTS servers MAY refuse mitigations with indefinite lifetimes, for policy reasons. The reasons themselves are out of scope for this document, but MUST be included in the mitigation rejection message from the server, per SIG-005.

SIG-007 Mitigation Scope: DOTS clients MUST indicate desired mitigation scope. The scope type will vary depending on the resources requiring mitigation. All DOTS agent implementations MUST support the following required scope types:

* IPv4 addresses in dotted quad format

* IPv4 prefixes in CIDR notation [RFC4632]

* IPv6 addresses [RFC4291][RFC5952]

* IPv6 prefixes [RFC4291][RFC5952]

* Domain names [RFC1035]

The following mitigation scope types are OPTIONAL:

* Uniform Resource Identifiers [RFC3986]

DOTS agents MUST support mitigation scope aliases, allowing DOTS client and server to refer to collections of protected resources by an opaque identifier created through the data channel, direct configuration, or other means. Domain name and URI mitigation scopes may be thought of as a form of scope alias, in which the addresses to which the domain name or URI resolve represent the full scope of the mitigation.

If there is additional information available narrowing the scope of any requested attack response, such as targeted port range,



protocol, or service, DOTS clients SHOULD include that information in client signals. DOTS clients MAY also include additional attack details. Such supplemental information is OPTIONAL, and DOTS servers MAY ignore it when enabling countermeasures on the mitigator.

As an active attack evolves, clients MUST be able to adjust as necessary the scope of requested mitigation by refining the scope of resources requiring mitigation.

SIG-008 Mitigation Efficacy: When a mitigation request by a DOTS client is active, DOTS clients SHOULD transmit a metric of perceived mitigation efficacy to the DOTS server. DOTS servers MAY use the efficacy metric to adjust countermeasures activated on a mitigator on behalf of a DOTS client.

SIG-009 Conflict Detection and Notification: Multiple DOTS clients controlled by a single administrative entity may send conflicting mitigation requests for pool of protected resources , as a result of misconfiguration, operator error, or compromised DOTS clients. DOTS servers attempting to honor conflicting requests may flap network route or DNS information, degrading the networks attempting to participate in attack response with the DOTS clients. DOTS servers SHALL detect such conflicting requests, and SHALL notify the DOTS clients in conflict. The notification SHOULD indicate the nature and scope of the conflict, for example, the overlapping prefix range in a conflicting mitigation request.

SIG-010: Network Address Translator Traversal: DOTS clients may be deployed behind a Network Address Translator (NAT), and need to communicate with DOTS servers through the NAT. DOTS protocols MUST therefore be capable of traversing NATs.

If UDP is used as the transport for the DOTS signal channel, all considerations in "Middlebox Traversal Guidelines" in [RFC5405] apply to DOTS. Regardless of transport, DOTS protocols MUST follow established best common practices (BCPs) for NAT traversal.

2.3. Data Channel Requirements

The data channel is intended to be used for bulk data exchanges between DOTS agents. Unlike the signal channel, which must operate nominally even when confronted with signal degradation due to packet loss, the data channel is not expected to be constructed to deal with attack conditions. As the primary function of the data channel is data exchange, a reliable transport is required in order for DOTS agents to detect data delivery success or failure.



The data channel must be extensible. We anticipate the data channel will be used for such purposes as configuration or resource discovery. For example, a DOTS client may submit to the DOTS server a collection of prefixes it wants to refer to by alias when requesting mitigation, to which the server would respond with a success status and the new prefix group alias, or an error status and message in the event the DOTS client’s data channel request failed. The transactional nature of such data exchanges suggests a separate set of requirements for the data channel, while the potentially sensitive content sent between DOTS agents requires extra precautions to ensure data privacy and authenticity.

DATA-001 Reliable transport: Messages sent over the data channel MUST be delivered reliably, in order sent.

DATA-002 Data privacy and integrity: Transmissions over the data channel are likely to contain operationally or privacy-sensitive information or instructions from the remote DOTS agent. Theft or modification of data channel transmissions could lead to information leaks or malicious transactions on behalf of the sending agent (see Section 4 below). Consequently data sent over the data channel MUST be encrypted and authenticated using current industry best practices. DOTS servers MUST enable means to prevent leaking operationally or privacy-sensitive data. Although administrative entities participating in DOTS may detail what data may be revealed to third-party DOTS agents, such considerations are not in scope for this document.

DATA-003 Resource Configuration: To help meet the general and signal channel requirements in this document, DOTS server implementations MUST provide an interface to configure resource identifiers, as described in SIG-007. DOTS server implementations MAY expose additional configurability. Additional configurability is implementation-specific.

DATA-004 Black- and whitelist management: DOTS servers MUST provide methods for DOTS clients to manage black- and white-lists of traffic destined for resources belonging to a client.

For example, a DOTS client should be able to create a black- or whitelist entry; retrieve a list of current entries from either list; update the content of either list; and delete entries as necessary.

How the DOTS server authorizes DOTS client management of black- and white-list entries is implementation-specific.



2.4. Security requirements

DOTS must operate within a particularly strict security context, as an insufficiently protected signal or data channel may be subject to abuse, enabling or supplementing the very attacks DOTS purports to mitigate.

SEC-001 Peer Mutual Authentication: DOTS agents MUST authenticate each other before a DOTS signal or data channel is considered valid. The method of authentication is not specified, but should follow current industry best practices with respect to any cryptographic mechanisms to authenticate the remote peer.

SEC-002 Message Confidentiality, Integrity and Authenticity: DOTS protocols MUST take steps to protect the confidentiality, integrity and authenticity of messages sent between client and server. While specific transport- and message-level security options are not specified, the protocols MUST follow current industry best practices for encryption and message authentication.

In order for DOTS protocols to remain secure despite advancements in cryptanalysis and traffic analysis, DOTS agents MUST be able to negotiate the terms and mechanisms of protocol security, subject to the interoperability and signal message size requirements above.

While the interfaces between downstream DOTS server and upstream DOTS client within a DOTS gateway are implementation-specific, those interfaces nevertheless MUST provide security equivalent to that of the signal channels bridged by gateways in the signaling path. For example, when a DOTS gateway consisting of a DOTS server and DOTS client is running on the same logical device, they must be within the same process security boundary.

SEC-003 Message Replay Protection: To prevent a passive attacker from capturing and replaying old messages, and thereby potentially disrupting or influencing the network policy of the receiving DOTS agent’s domain, DOTS protocols MUST provide a method for replay detection and prevention.

Within the signal channel, messages MUST be uniquely identified such that replayed or duplicated messages may be detected and discarded. Unique mitigation requests MUST be processed at most once.

SEC-004 Authorization: DOTS servers MUST authorize all messages from DOTS clients which pertain to mitigation, configuration, filtering, or status.



DOTS servers MUST reject mitigation requests with scopes which the DOTS client is not authorized to manage.

Likewise, DOTS servers MUST refuse to allow creation, modification or deletion of scope aliases and black-/white-lists when the DOTS client is unauthorized.

The modes of authorization are implementation-specific.

2.5. Data Model Requirements

The value of DOTS is in standardizing a mechanism to permit elements, networks or domains under or under threat of DDoS attack to request aid mitigating the effects of any such attack. A well-structured DOTS data model is therefore critical to the development of a successful DOTS protocol.

DM-001: Structure: The data model structure for the DOTS protocol may be described by a single module, or be divided into related collections of hierarchical modules and sub-modules. If the data model structure is split across modules, those distinct modules MUST allow references to describe the overall data model’s structural dependencies.

DM-002: Versioning: To ensure interoperability between DOTS protocol implementations, data models MUST be versioned. The version number of the initial data model SHALL be 1. Each published change to the initial published DOTS data model SHALL increment the data model version by 1.

How the protocol represents data model versions is not defined in this document.

DM-003: Mitigation Status Representation: The data model MUST provide the ability to represent a request for mitigation and the withdrawal of such a request. The data model MUST also support a representation of currently requested mitigation status, including failures and their causes.

DM-004: Mitigation Scope Representation: The data model MUST support representation of a requested mitigation’s scope. As mitigation scope may be represented in several different ways, per SIG-007 above, the data model MUST be capable of flexible representation of mitigation scope.

DM-005: Mitigation Lifetime Representation: The data model MUST support representation of a mitigation request’s lifetime, including mitigations with no specified end time.



DM-006: Mitigation Efficacy Representation: The data model MUST support representation of a DOTS client’s understanding of the efficacy of a mitigation enabled through a mitigation request.

DM-007: Acceptable Signal Loss Representation: The data model MUST be able to represent the DOTS agent’s preference for acceptable signal loss when establishing a signal channel, as described in GEN-002.

DM-008: Heartbeat Interval Representation: The data model MUST be able to represent the DOTS agent’s preferred heartbeat interval, which the client may include when establishing the signal channel, as described in SIG-003.

DM-009: Relationship to Transport: The DOTS data model MUST NOT depend on the specifics of any transport to represent fields in the model.

3. Congestion Control Considerations

3.1. Signal Channel

As part of a protocol expected to operate over links affected by DDoS attack traffic, the DOTS signal channel MUST NOT contribute significantly to link congestion. To meet the signal channel requirements above, DOTS signal channel implementations SHOULD support connectionless transports. However, some connectionless transports when deployed naively can be a source of network congestion, as discussed in [RFC5405]. Signal channel implementations using such connectionless transports, such as UDP, therefore MUST include a congestion control mechanism.

Signal channel implementations using TCP may rely on built-in TCP congestion control support.

3.2. Data Channel

As specified in DATA-001, the data channel requires reliable, in- order message delivery. Data channel implementations using TCP may rely on the TCP implementation’s built-in congestion control mechanisms.


DOTS is at risk from three primary attacks:

o DOTS agent impersonation



o Traffic injection

o Signaling blocking

The DOTS protocol MUST be designed for minimal data transfer to address the blocking risk. Impersonation and traffic injection mitigation can be managed through current secure communications best practices. See Section 2.4 above for a detailed discussion.

5. Contributors


[email protected]

Flemming Andreasen Cisco Systems, Inc.

[email protected]

Dave Dolson Sandvine

[email protected]

6. Acknowledgments

Thanks to Roman Danyliw and Matt Richardson for careful reading and feedback.

7. Change Log

7.1. 04 revision

2017-03-13

o Establish required and optional mitigation scope types

o Specify message size for DOTS signal channel

o Recast mitigation lifetime as a DOTS server requirement

o Clarify DOTS server’s responsibilities after client request to end mitigation

o Specify security state handling on redirection



o Signal channel should use transport not susceptible to HOL blocking

o Expanded list of DDoS types to include network links

7.2. 03 revision

2016-10-30

o Extended SEC-003 to require secure interfaces within DOTS gateways.

o Changed DATA-003 to Resource Configuration, delegating control of acceptable signal loss, heartbeat intervals, and mitigation lifetime to DOTS client.

o Added data model requirements reflecting client control over the above.

7.3. 02 revision

7.4. 01 revision

2016-03-21

o Reconciled terminology with -00 revision of [I-D.ietf-dots-use-cases].

o Terminology clarification based on working group feedback.

o Moved security-related requirements to separate section.

o Made resilience/robustness primary general requirement to align with charter.

o Clarified support for unidirectional communication within the bidirectional signal channel.

o Added proposed operational requirement to support session redirection.

o Added proposed operational requirement to support conflict notification.

o Added proposed operational requirement to support mitigation lifetime in mitigation requests.



o Added proposed operational requirement to support mitigation efficacy reporting from DOTS clients.

o Added proposed operational requirement to cache lookups of all kinds.

o Added proposed operational requirement regarding NAT traversal.

o Removed redundant mutual authentication requirement from data channel requirements.

7.5. 00 revision

2015-10-15

7.6. Initial revision

2015-09-24 Andrew Mortensen

8. References


[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI 10.17487/RFC0768, August 1980, <http://www.rfc-editor.org/info/rfc768>.

[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 10.17487/RFC0791, September 1981, <http://www.rfc-editor.org/info/rfc791>.

[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, DOI 10.17487/RFC0793, September 1981, <http://www.rfc-editor.org/info/rfc793>.

[RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, <http://www.rfc-editor.org/info/rfc1035>.

[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, DOI 10.17487/RFC1122, October 1989, <http://www.rfc-editor.org/info/rfc1122>.

[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, DOI 10.17487/RFC1191, November 1990, <http://www.rfc-editor.org/info/rfc1191>.




[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, <http://www.rfc-editor.org/info/rfc3986>.

[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006, <http://www.rfc-editor.org/info/rfc4291>.

[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 2006, <http://www.rfc-editor.org/info/rfc4632>.

[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, <http://www.rfc-editor.org/info/rfc4821>.

[RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines for Application Designers", RFC 5405, DOI 10.17487/RFC5405, November 2008, <http://www.rfc-editor.org/info/rfc5405>.

[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 Address Text Representation", RFC 5952, DOI 10.17487/RFC5952, August 2010, <http://www.rfc-editor.org/info/rfc5952>.






[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, DOI 10.17487/RFC3261, June 2002, <http://www.rfc-editor.org/info/rfc3261>.



Andrew Mortensen Arbor Networks 2727 S. State St Ann Arbor, MI 48104 United States


Robert Moskowitz HTT Consulting Oak Park, MI 42837 United States





DOTS A. Mortensen

Internet-Draft Arbor Networks

Intended status: Informational T. Reddy

Expires: September 24, 2019 McAfee

R. Moskowitz

Huawei

March 23, 2019

Distributed Denial of Service (DDoS) Open Threat Signaling Requirements

draft-ietf-dots-requirements-22

Abstract

This document defines the requirements for the Distributed Denial of

Service (DDoS) Open Threat Signaling (DOTS) protocols enabling

coordinated response to DDoS attacks.

Status of This Memo

This Internet-Draft is submitted in full conformance with the

provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering

Task Force (IETF). Note that other groups may also distribute

working documents as Internet-Drafts. The list of current Internet-

Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months

and may be updated, replaced, or obsoleted by other documents at any

time. It is inappropriate to use Internet-Drafts as reference

material or to cite them other than as "work in progress."

This Internet-Draft will expire on September 24, 2019.

Copyright Notice

Copyright (c) 2019 IETF Trust and the persons identified as the

document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust’s Legal

Provisions Relating to IETF Documents

(https://trustee.ietf.org/license-info) in effect on the date of

publication of this document. Please review these documents

carefully, as they describe your rights and restrictions with respect

to this document. Code Components extracted from this document must

include Simplified BSD License text as described in Section 4.e of


Internet-Draft DOTS Requirements March 2019

the Trust Legal Provisions and are provided without warranty as

described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2

1.1. Context and Motivation . . . . . . . . . . . . . . . . . 2

1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3

2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5

2.1. General Requirements . . . . . . . . . . . . . . . . . . 7

2.2. Signal Channel Requirements . . . . . . . . . . . . . . . 8

2.3. Data Channel Requirements . . . . . . . . . . . . . . . . 13

2.4. Security Requirements . . . . . . . . . . . . . . . . . . 14

2.5. Data Model Requirements . . . . . . . . . . . . . . . . . 16

3. Congestion Control Considerations . . . . . . . . . . . . . . 17

3.1. Signal Channel . . . . . . . . . . . . . . . . . . . . . 17

3.2. Data Channel . . . . . . . . . . . . . . . . . . . . . . 17

4. Security Considerations . . . . . . . . . . . . . . . . . . . 17

5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18

6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 18

7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19

8. References . . . . . . . . . . . . . . . . . . . . . . . . . 19

8.1. Normative References . . . . . . . . . . . . . . . . . . 19

8.2. Informative References . . . . . . . . . . . . . . . . . 20

Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 21

1. Introduction

1.1. Context and Motivation

Distributed Denial of Service (DDoS) attacks afflict networks

connected to the Internet, plaguing network operators at service

providers and enterprises around the world. High-volume attacks

saturating inbound links are now common, as attack scale and

frequency continue to increase.

The prevalence and impact of these DDoS attacks has led to an

increased focus on coordinated attack response. However, many

enterprises lack the resources or expertise to operate on-premises

attack mitigation solutions themselves, or are constrained by local

bandwidth limitations. To address such gaps, service providers have

begun to offer on-demand traffic scrubbing services, which are

designed to separate the DDoS attack traffic from legitimate traffic

and forward only the latter.

Today, these services offer proprietary interfaces for subscribers to

request attack mitigation. Such proprietary interfaces tie a

subscriber to a service and limit the abilities of network elements



that would otherwise be capable of participating in attack

mitigation. As a result of signaling interface incompatibility,

attack responses may be fragmented or otherwise incomplete, leaving

operators in the attack path unable to assist in the defense.

A standardized method to coordinate a real-time response among

involved operators will increase the speed and effectiveness of DDoS

attack mitigation, and reduce the impact of these attacks. This

document describes the required characteristics of protocols that

enable attack response coordination and mitigation of DDoS attacks.

DDoS Open Threat Signaling (DOTS) communicates the need for defensive

action in anticipation of or in response to an attack, but does not

dictate the implementation of these actions. The DOTS use cases are

discussed in [I-D.ietf-dots-use-cases] and the DOTS architecture is

discussed in [I-D.ietf-dots-architecture].

1.2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",

"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this

document are to be interpreted as described in BCP14 [RFC2119]

[RFC8174], when, and only when, they appear in all capitals. These

capitalized words are used to signify the requirements for DOTS

protocols design.

This document adopts the following terms:

DDoS: A distributed denial-of-service attack, in which traffic

originating from multiple sources is directed at a target on a

network. DDoS attacks are intended to cause a negative impact on

the availability and/or other functionality of an attack target.

Denial-of-service considerations are discussed in detail in

[RFC4732].

DDoS attack target: A network connected entity that is the target of

a DDoS attack. Potential targets include (but are not limited to)

network elements, network links, servers, and services.

DDoS attack telemetry: Collected measurements and behavioral

characteristics defining the nature of a DDoS attack.

Countermeasure: An action or set of actions focused on recognizing

and filtering out specific types of DDoS attack traffic while

passing legitimate traffic to the attack target. Distinct

countermeasures can be layered to defend against attacks combining

multiple DDoS attack types.



Mitigation: A set of countermeasures enforced against traffic

destined for the target or targets of a detected or reported DDoS

attack, where countermeasure enforcement is managed by an entity

in the network path between attack sources and the attack target.

Mitigation methodology is out of scope for this document.

Mitigator: An entity, typically a network element, capable of

performing mitigation of a detected or reported DDoS attack. The

means by which this entity performs these mitigations and how they

are requested of it are out of scope for this document. The

mitigator and DOTS server receiving a mitigation request are

assumed to belong to the same administrative entity.

DOTS client: A DOTS-aware software module responsible for requesting

attack response coordination with other DOTS-aware elements.

DOTS server: A DOTS-aware software module handling and responding to

messages from DOTS clients. The DOTS server enables mitigation on

behalf of the DOTS client, if requested, by communicating the DOTS

client’s request to the mitigator and returning selected mitigator

feedback to the requesting DOTS client.

DOTS agent: Any DOTS-aware software module capable of participating

in a DOTS signal or data channel. It can be a DOTS client, DOTS

server, or, as a logical agent, a DOTS gateway.

DOTS gateway: A DOTS-aware software module resulting from the

logical concatenation of the functionality of a DOTS server and a

DOTS client into a single DOTS agent. This functionality is

analogous to a Session Initiation Protocol (SIP) [RFC3261] Back-

to-Back User Agent (B2BUA) [RFC7092]. A DOTS gateway has a

client-facing side, which behaves as a DOTS server for downstream

clients, and a server-facing side, which performs the role of DOTS

client for upstream DOTS servers. Client-domain DOTS gateways are

DOTS gateways that are in the DOTS client’s domain, while server-

domain DOTS gateways denote DOTS gateways that are in the DOTS

server’s domain. A DOTS gateway may terminate multiple discrete

DOTS client connections and may aggregate these into a single or

multiple connections. DOTS gateways are described further in

[I-D.ietf-dots-architecture].

Signal channel: A bidirectional, mutually authenticated

communication channel between DOTS agents that is resilient even

in conditions leading to severe packet loss, such as a volumetric

DDoS attack causing network congestion.

DOTS signal: A status/control message transmitted over the

authenticated signal channel between DOTS agents, used to indicate



the client’s need for mitigation, or to convey the status of any

requested mitigation.

Heartbeat: A message transmitted between DOTS agents over the signal

channel, used as a keep-alive and to measure peer health.

Data channel: A bidirectional, mutually authenticated communication

channel between two DOTS agents used for infrequent but reliable

bulk exchange of data not easily or appropriately communicated

through the signal channel. Reliable bulk data exchange may not

function well or at all during attacks causing network congestion.

The data channel is not expected to operate in such conditions.

Filter: A specification of a matching network traffic flow or set of

flows. The filter will typically have a policy associated with

it, e.g., rate-limiting or discarding matching traffic [RFC4949].

Drop-list: A list of filters indicating sources from which traffic

should be blocked, regardless of traffic content.

Accept-list: A list of filters indicating sources from which traffic

should always be allowed, regardless of contradictory data gleaned

in a detected attack.

Multi-homed DOTS client: A DOTS client exchanging messages with

multiple DOTS servers, each in a separate administrative domain.

2. Requirements

The expected layout and interactions amongst DOTS entities is

described in the DOTS Architecture [I-D.ietf-dots-architecture].

The goal of the DOTS requirements specification is to specify the

requirements for DOTS signal channel and data channel protocols that

have different application and transport layer requirements. This

section describes the required features and characteristics of the

DOTS protocols.

The goal of DOTS protocols is to enable and manage mitigation on

behalf of a network domain or resource which is or may become the

focus of a DDoS attack. An active DDoS attack against the entity

controlling the DOTS client need not be present before establishing a

communication channel between DOTS agents. Indeed, establishing a

relationship with peer DOTS agents during normal network conditions

provides the foundation for more rapid attack response against future

attacks, as all interactions setting up DOTS, including any business

or service level agreements, are already complete. Reachability

information of peer DOTS agents is provisioned to a DOTS client using



a variety of manual or dynamic methods. Once a relationship between

DOTS agents is established, regular communication between DOTS

clients and servers enables a common understanding of the DOTS

agents’ health and activity.

The DOTS protocol must at a minimum make it possible for a DOTS

client to request aid mounting a defense against a suspected attack.

This defense could be coordinated by a DOTS server and include

signaling within or between domains as requested by local operators.

DOTS clients should similarly be able to withdraw aid requests. DOTS

requires no justification from DOTS clients for requests for help,

nor do DOTS clients need to justify withdrawing help requests: the

decision is local to the DOTS clients’ domain. Multi-homed DOTS

clients must be able to select the appropriate DOTS server(s) to

which a mitigation request is to be sent. The method for selecting

the appropriate DOTS server in a multi-homed environment is out of

scope for this document.

DOTS protocol implementations face competing operational goals when

maintaining this bidirectional communication stream. On the one

hand, DOTS must include measures to ensure message confidentiality,

integrity, authenticity, and replay protection to keep the protocols

from becoming additional vectors for the very attacks it is meant to

help fight off. On the other hand, the protocol must be resilient

under extremely hostile network conditions, providing continued

contact between DOTS agents even as attack traffic saturates the

link. Such resiliency may be developed several ways, but

characteristics such as small message size, asynchronous, redundant

message delivery and minimal connection overhead (when possible given

local network policy) will tend to contribute to the robustness

demanded by a viable DOTS protocol. Operators of peer DOTS-enabled

domains may enable quality- or class-of-service traffic tagging to

increase the probability of successful DOTS signal delivery, but DOTS

does not require such policies be in place, and should be viable in

their absence.

The DOTS server and client must also have some standardized method of

defining the scope of any mitigation, as well as managing other

mitigation-related configuration.

Finally, DOTS should be sufficiently extensible to meet future needs

in coordinated attack defense, although this consideration is

necessarily superseded by the other operational requirements.



2.1. General Requirements

GEN-001 Extensibility: Protocols and data models developed as part

of DOTS MUST be extensible in order to keep DOTS adaptable to

proprietary DDoS defenses. Future extensions MUST be backward

compatible. Implementations of older protocol versions MUST

ignore optional information added to DOTS messages as part of

newer protocol versions. Implementations of older protocol

versions MUST reject DOTS messages carrying mandatory information

as part of newer protocol versions.

GEN-002 Resilience and Robustness: The signaling protocol MUST be

designed to maximize the probability of signal delivery even under

the severely constrained network conditions caused by attack

traffic. Additional means to enhance the resilience of DOTS

protocols, including when multiple DOTS servers are provisioned to

the DOTS clients, SHOULD be considered. The protocol MUST be

resilient, that is, continue operating despite message loss and

out-of-order or redundant message delivery. In support of

signaling protocol robustness, DOTS signals SHOULD be conveyed

over transport and application protocols not susceptible to Head

of Line Blocking. These requirements are at SHOULD strength to

handle middle-boxes and firewall traversal.

GEN-003 Bulk Data Exchange: Infrequent bulk data exchange between

DOTS agents can also significantly augment attack response

coordination, permitting such tasks as population of drop- or

accept-listed source addresses; address or prefix group aliasing;

exchange of incident reports; and other hinting or configuration

supplementing attack response.

As the resilience requirements for the DOTS signal channel mandate

small signal message size, a separate, secure data channel

utilizing a reliable transport protocol MUST be used for bulk data

exchange. However, reliable bulk data exchange may not be

possible during attacks causing network congestion.

GEN-004 Mitigation Hinting: DOTS clients may have access to attack

details which can be used to inform mitigation techniques.

Example attack details might include locally collected

fingerprints for an on-going attack, or anticipated or active

attack focal points based on other threat intelligence. DOTS

clients MAY send mitigation hints derived from attack details to

DOTS servers, in the full understanding that the DOTS server MAY

ignore mitigation hints. Mitigation hints MUST be transmitted

across the signal channel, as the data channel may not be

functional during an attack. DOTS server handling of mitigation

hints is implementation-specific.



GEN-005 Loop Handling: In certain scenarios, typically involving

misconfiguration of DNS or routing policy, it may be possible for

communication between DOTS agents to loop. Signal and data

channel implementations should be prepared to detect and terminate

such loops to prevent service disruption.

2.2. Signal Channel Requirements

SIG-001 Use of Common Transport Protocols: DOTS MUST operate over

common widely deployed and standardized transport protocols.

While connectionless transport such as the User Datagram Protocol

(UDP) [RFC0768] SHOULD be used for the signal channel, the

Transmission Control Protocol (TCP) [RFC0793] MAY be used if

necessary due to network policy or middlebox capabilities or

configurations.

SIG-002 Sub-MTU Message Size: To avoid message fragmentation and the

consequently decreased probability of message delivery over a

congested link, signaling protocol message size MUST be kept under

signaling Path Maximum Transmission Unit (PMTU), including the

byte overhead of any encapsulation, transport headers, and

transport- or message-level security. If the total message size

exceeds the path MTU, the DOTS agent MUST split the message into

separate messages; for example, the list of mitigation scope types

could be split into multiple lists and each list conveyed in a new

message.

DOTS agents can attempt to learn PMTU using the procedures

discussed in [I-D.ietf-intarea-frag-fragile]. If the PMTU cannot

be discovered, DOTS agents MUST assume a PMTU of 1280 bytes, as

IPv6 requires that every link in the Internet have an MTU of 1280

octets or greater as specified in [RFC8200]. If IPv4 support on

legacy or otherwise unusual networks is a consideration and the

PMTU is unknown, DOTS implementations MAY assume on a PMTU of 576

bytes for IPv4 datagrams, as every IPv4 host must be capable of

receiving a packet whose length is equal to 576 bytes as discussed

in [RFC0791] and [RFC1122].

SIG-003 Bidirectionality: To support peer health detection, to

maintain an active signal channel, and to increase the probability

of signal delivery during an attack, the signal channel MUST be

bidirectional, with client and server transmitting signals to each

other at regular intervals, regardless of any client request for

mitigation. The bidirectional signal channel MUST support

unidirectional messaging to enable notifications between DOTS

agents.



SIG-004 Channel Health Monitoring: DOTS agents MUST support exchange

of heartbeat messages over the signal channel to monitor channel

health. These keepalives serve the purpose to maintain any on-

path NAT or Firewall bindings to avoid cryptographic handshake for

new mitigation requests. The heartbeat interval during active

mitigation could be negotiable based on NAT/Firewall

characteristics. Absent information about the NAT/Firewall

characteristics, DOTS agent needs to ensure its on-path NAT or

Firewall bindings do not expire, by using the keep-alive frequency

discussed in Section 3.5 of [RFC8085].

To support scenarios in which loss of heartbeat is used to trigger

mitigation, and to keep the channel active, DOTS servers MUST

solicit heartbeat exchanges after successful mutual

authentication. When DOTS agents are exchanging heartbeats and no

mitigation request is active, either agent MAY request changes to

the heartbeat rate. For example, a DOTS server might want to

reduce heartbeat frequency or cease heartbeat exchanges when an

active DOTS client has not requested mitigation, in order to

control load.

Following mutual authentication, a signal channel MUST be

considered active until a DOTS agent explicitly ends the session.

When no attack traffic is present, the signal channel MUST be

considered active until either DOTS agent fails to receive

heartbeats from the other peer after a mutually agreed upon

retransmission procedure has been exhausted. Peer DOTS agents

MUST regularly send heartbeats to each other while a mitigation

request is active. Because heartbeat loss is much more likely

during volumetric attack, DOTS agents SHOULD avoid signal channel

termination when mitigation is active and heartbeats are not

received by either DOTS agent for an extended period. The

exception circumstances to terminate the signal channel session

during active mitigation are discussed below:

* To handle possible DOTS server restart or crash, the DOTS

clients MAY attempt to establish a new signal channel session,

but MUST continue to send heartbeats on the current session so

that the DOTS server knows the session is still alive. If the

new session is successfully established, the DOTS client can

terminate the current session.

* DOTS servers are assumed to have the ability to monitor the

attack, using feedback from the mitigator and other available

sources, and MAY use the absence of attack traffic and lack of



client heartbeats as an indication the signal channel is

defunct.

SIG-005 Channel Redirection: In order to increase DOTS operational

flexibility and scalability, DOTS servers SHOULD be able to

redirect DOTS clients to another DOTS server at any time. DOTS

clients MUST NOT assume the redirection target DOTS server shares

security state with the redirecting DOTS server. DOTS clients are

free to attempt abbreviated security negotiation methods supported

by the protocol, such as DTLS session resumption, but MUST be

prepared to negotiate new security state with the redirection

target DOTS server. The redirection DOTS server and redirecting

DOTS server MUST belong to the same administrative domain.

Due to the increased likelihood of packet loss caused by link

congestion during an attack, DOTS servers SHOULD NOT redirect

while mitigation is enabled during an active attack against a

target in the DOTS client’s domain.

SIG-006 Mitigation Requests and Status: Authorized DOTS clients MUST

be able to request scoped mitigation from DOTS servers. DOTS

servers MUST send status to the DOTS clients about mitigation

requests. If a DOTS server rejects an authorized request for

mitigation, the DOTS server MUST include a reason for the

rejection in the status message sent to the client.

DOTS servers MUST regularly send mitigation status updates to

authorized DOTS clients which have requested and been granted

mitigation. If unreliable transport is used for the signal

channel protocol, due to the higher likelihood of packet loss

during a DDoS attack, DOTS servers needs to send mitigation status

multiple times at regular intervals following the the data

transmission guidelines discussed in Section 3.1.3 of [RFC8085].

When DOTS client-requested mitigation is active, DOTS server

status messages MUST include the following mitigation metrics:

* Total number of packets blocked by the mitigation

* Current number of packets per second blocked

* Total number of bytes blocked

* Current number of bytes per second blocked

DOTS clients MAY take these metrics into account when determining

whether to ask the DOTS server to cease mitigation.



A DOTS client MAY withdraw a mitigation request at any time,

regardless of whether mitigation is currently active. The DOTS

server MUST immediately acknowledge a DOTS client’s request to

stop mitigation.

To protect against route or DNS flapping caused by a client

rapidly toggling mitigation, and to dampen the effect of

oscillating attacks, DOTS servers MAY allow mitigation to continue

for a limited period after acknowledging a DOTS client’s

withdrawal of a mitigation request. During this period, DOTS

server status messages SHOULD indicate that mitigation is active

but terminating. DOTS clients MAY reverse the mitigation

termination during this active-but-terminating period with a new

mitigation request for the same scope. The DOTS server MUST treat

this request as a mitigation lifetime extension (see SIG-007

below).

The initial active-but-terminating period is implementation- and

deployment- specific, but SHOULD be sufficiently long to absorb

latency incurred by route propagation. If a DOTS client refreshes

the mitigation before the active-but-terminating period elapses,

the DOTS server MAY increase the active-but-terminating period up

to a maximum of 300 seconds (5 minutes). After the active-but-

terminating period elapses, the DOTS server MUST treat the

mitigation as terminated, as the DOTS client is no longer

responsible for the mitigation.

SIG-007 Mitigation Lifetime: DOTS servers MUST support mitigations

for a negotiated time interval, and MUST terminate a mitigation

when the lifetime elapses. DOTS servers also MUST support renewal

of mitigation lifetimes in mitigation requests from DOTS clients,

allowing clients to extend mitigation as necessary for the

duration of an attack.

DOTS servers MUST treat a mitigation terminated due to lifetime

expiration exactly as if the DOTS client originating the

mitigation had asked to end the mitigation, including the active-

but-terminating period, as described above in SIG-005.

DOTS clients MUST include a mitigation lifetime in all mitigation

requests.

DOTS servers SHOULD support indefinite mitigation lifetimes,

enabling architectures in which the mitigator is always in the

traffic path to the resources for which the DOTS client is

requesting protection. DOTS clients MUST be prepared to not be

granted mitigations with indefinite lifetimes. DOTS servers MAY

refuse mitigations with indefinite lifetimes, for policy reasons.



The reasons themselves are out of scope. If the DOTS server does

not grant a mitigation request with an indefinite mitigation

lifetime, it MUST set the lifetime to a value that is configured

locally. That value MUST be returned in a reply to the requesting

DOTS client.

SIG-008 Mitigation Scope: DOTS clients MUST indicate desired

mitigation scope. The scope type will vary depending on the

resources requiring mitigation. All DOTS agent implementations

MUST support the following required scope types:

* IPv4 prefixes [RFC4632]

* IPv6 prefixes [RFC4291][RFC5952]

* Domain names [RFC1035]

The following mitigation scope types are OPTIONAL:

* Uniform Resource Identifiers [RFC3986]

DOTS servers MUST be able to resolve domain names and (when

supported) URIs. How name resolution is managed on the DOTS

server is implementation-specific.

DOTS agents MUST support mitigation scope aliases, allowing DOTS

clients and servers to refer to collections of protected resources

by an opaque identifier created through the data channel, direct

configuration, or other means. Domain name and URI mitigation

scopes may be thought of as a form of scope alias, in which the

addresses to which the domain name or URI resolve represent the

full scope of the mitigation.

If there is additional information available narrowing the scope

of any requested attack response, such as targeted port range,

protocol, or service, DOTS clients SHOULD include that information

in client mitigation requests. DOTS clients MAY also include

additional attack details. DOTS servers MAY ignore such

supplemental information when enabling countermeasures on the

mitigator.

As an active attack evolves, DOTS clients MUST be able to adjust

as necessary the scope of requested mitigation by refining the

scope of resources requiring mitigation.

A DOTS client may obtain the mitigation scope through direct

provisioning or through implementation-specific methods of



discovery. DOTS clients MUST support at least one mechanism to

obtain mitigation scope.

SIG-009 Mitigation Efficacy: When a mitigation request is active,

DOTS clients MUST be able to transmit a metric of perceived

mitigation efficacy to the DOTS server. DOTS servers MAY use the

efficacy metric to adjust countermeasures activated on a mitigator

on behalf of a DOTS client.

SIG-010 Conflict Detection and Notification: Multiple DOTS clients

controlled by a single administrative entity may send conflicting

mitigation requests as a result of misconfiguration, operator

error, or compromised DOTS clients. DOTS servers in the same

administrative domain attempting to honor conflicting requests may

flap network route or DNS information, degrading the networks

attempting to participate in attack response with the DOTS

clients. DOTS servers in a single administrative domain SHALL

detect such conflicting requests, and SHALL notify the DOTS

clients in conflict. The notification MUST indicate the nature

and scope of the conflict, for example, the overlapping prefix

range in a conflicting mitigation request.

SIG-011 Network Address Translator Traversal: DOTS clients may be

deployed behind a Network Address Translator (NAT), and need to

communicate with DOTS servers through the NAT. DOTS protocols

MUST therefore be capable of traversing NATs.

If UDP is used as the transport for the DOTS signal channel, all

considerations in "Middlebox Traversal Guidelines" in [RFC8085]

apply to DOTS. Regardless of transport, DOTS protocols MUST

follow established best common practices established in BCP 127

for NAT traversal [RFC4787][RFC6888][RFC7857].

2.3. Data Channel Requirements

The data channel is intended to be used for bulk data exchanges

between DOTS agents. Unlike the signal channel, the data channel is

not expected to be constructed to deal with attack conditions. As

the primary function of the data channel is data exchange, a reliable

transport is required in order for DOTS agents to detect data

delivery success or failure.

The data channel provides a protocol for DOTS configuration,

management. For example, a DOTS client may submit to a DOTS server a

collection of prefixes it wants to refer to by alias when requesting

mitigation, to which the server would respond with a success status

and the new prefix group alias, or an error status and message in the

event the DOTS client’s data channel request failed.



DATA-001 Reliable transport: Messages sent over the data channel

MUST be delivered reliably, in order sent.

DATA-003 Resource Configuration: To help meet the general and signal

channel requirements in Section 2.1 and Section 2.2, DOTS server

implementations MUST provide an interface to configure resource

identifiers, as described in SIG-008. DOTS server implementations

MAY expose additional configurability. Additional configurability

is implementation-specific.

DATA-004 Policy management: DOTS servers MUST provide methods for

DOTS clients to manage drop- and accept-lists of traffic destined

for resources belonging to a client.

For example, a DOTS client should be able to create a drop- or

accept-list entry, retrieve a list of current entries from either

list, update the content of either list, and delete entries as

necessary.

How a DOTS server authorizes DOTS client management of drop- and

accept-list entries is implementation-specific.

2.4. Security Requirements

DOTS must operate within a particularly strict security context, as

an insufficiently protected signal or data channel may be subject to

abuse, enabling or supplementing the very attacks DOTS purports to

mitigate.

SEC-001 Peer Mutual Authentication: DOTS agents MUST authenticate

each other before a DOTS signal or data channel is considered

valid. The method of authentication is not specified in this

document, but should follow current IETF best practices [RFC7525]

with respect to any cryptographic mechanisms to authenticate the

remote peer.

SEC-002 Message Confidentiality, Integrity and Authenticity: DOTS

protocols MUST take steps to protect the confidentiality,

integrity and authenticity of messages sent between client and

server. While specific transport- and message-level security

options are not specified, the protocols MUST follow current IETF

best practices [RFC7525] for encryption and message

authentication. Client-domain DOTS gateways are more trusted than

DOTS clients, while server-domain DOTS gateways and DOTS servers

share the same level of trust. A security mechanism at the

transport layer TLS/DTLS is thus adequate to provide security

between peer DOTS agents.



In order for DOTS protocols to remain secure despite advancements

in cryptanalysis and traffic analysis, DOTS agents MUST support

secure negotiation of the terms and mechanisms of protocol

security, subject to the interoperability and signal message size

requirements in Section 2.2.

While the interfaces between downstream DOTS server and upstream

DOTS client within a DOTS gateway are implementation-specific,

those interfaces nevertheless MUST provide security equivalent to

that of the signal channels bridged by gateways in the signaling

path. For example, when a DOTS gateway consisting of a DOTS

server and DOTS client is running on the same logical device, the

two DOTS agents could be implemented within the same process

security boundary.

SEC-003 Data privacy and integrity: Transmissions over the DOTS

protocols are likely to contain operationally or privacy-sensitive

information or instructions from the remote DOTS agent. Theft,

modification, or replay of message transmissions could lead to

information leaks or malicious transactions on behalf of the

sending agent (see Section 4 below). Consequently data sent over

the DOTS protocols MUST be encrypted using secure transports TLS/

DTLS. DOTS servers MUST enable means to prevent leaking

operationally or privacy-sensitive data. Although administrative

entities participating in DOTS may detail what data may be

revealed to third-party DOTS agents, such considerations are not

in scope for this document.

SEC-004 Message Replay Protection: To prevent a passive attacker

from capturing and replaying old messages, and thereby potentially

disrupting or influencing the network policy of the receiving DOTS

agent’s domain, DOTS protocols MUST provide a method for replay

detection and prevention.

Within the signal channel, messages MUST be uniquely identified

such that replayed or duplicated messages can be detected and

discarded. Unique mitigation requests MUST be processed at most

once.

SEC-005 Authorization: DOTS servers MUST authorize all messages from

DOTS clients which pertain to mitigation, configuration,

filtering, or status.

DOTS servers MUST reject mitigation requests with scopes which the

DOTS client is not authorized to manage.



Likewise, DOTS servers MUST refuse to allow creation, modification

or deletion of scope aliases and drop-/accept-lists when the DOTS

client is unauthorized.

The modes of authorization are implementation-specific.

2.5. Data Model Requirements

A well-structured DOTS data model is critical to the development of

successful DOTS protocols.

DM-001 Structure: The data model structure for the DOTS protocol MAY

be described by a single module, or be divided into related

collections of hierarchical modules and sub-modules. If the data

model structure is split across modules, those distinct modules

MUST allow references to describe the overall data model’s

structural dependencies.

DM-002 Versioning: To ensure interoperability between DOTS protocol

implementations, data models MUST be versioned. How the protocols

represent data model versions is not defined in this document.

DM-003 Mitigation Status Representation: The data model MUST provide

the ability to represent a request for mitigation and the

withdrawal of such a request. The data model MUST also support a

representation of currently requested mitigation status, including

failures and their causes.

DM-004 Mitigation Scope Representation: The data model MUST support

representation of a requested mitigation’s scope. As mitigation

scope may be represented in several different ways, per SIG-008

above, the data model MUST include extensible representation of

mitigation scope.

DM-005 Mitigation Lifetime Representation: The data model MUST

support representation of a mitigation request’s lifetime,

including mitigations with no specified end time.

DM-006 Mitigation Efficacy Representation: The data model MUST

support representation of a DOTS client’s understanding of the

efficacy of a mitigation enabled through a mitigation request.

DM-007 Acceptable Signal Loss Representation: The data model MUST be

able to represent the DOTS agent’s preference for acceptable

signal loss when establishing a signal channel. Measurements of

loss might include, but are not restricted to, number of

consecutive missed heartbeat messages, retransmission count, or

request timeouts.



DM-008 Heartbeat Interval Representation: The data model MUST be

able to represent the DOTS agent’s preferred heartbeat interval,

which the client may include when establishing the signal channel,

as described in SIG-003.

DM-009 Relationship to Transport: The DOTS data model MUST NOT make

any assumptions about specific characteristics of any given

transport into the data model, but instead, represent the fields

in the model explicitly.

3. Congestion Control Considerations

3.1. Signal Channel

As part of a protocol expected to operate over links affected by DDoS

attack traffic, the DOTS signal channel MUST NOT contribute

significantly to link congestion. To meet the signal channel

requirements above, DOTS signal channel implementations SHOULD

support connectionless transports. However, some connectionless

transports when deployed naively can be a source of network

congestion, as discussed in [RFC8085]. Signal channel

implementations using such connectionless transports, such as UDP,

therefore MUST include a congestion control mechanism.

Signal channel implementations using a IETF standard congestion-

controlled transport protocol (like TCP) may rely on built-in

transport congestion control support.

3.2. Data Channel

As specified in DATA-001, the data channel requires reliable, in-

order message delivery. Data channel implementations using a IETF

standard congestion-controlled transport protocol may rely on the

transport implementation’s built-in congestion control mechanisms.


This document informs future protocols under development, and so does

not have security considerations of its own. However, operators

should be aware of potential risks involved in deploying DOTS. DOTS

agent impersonation and signal blocking are discussed here.

Additional DOTS security considerations may be found in

[I-D.ietf-dots-architecture] and DOTS protocol documents.

Impersonation of either a DOTS server or a DOTS client could have

catastrophic impact on operations in either domain. If an attacker

has the ability to impersonate a DOTS client, that attacker can

affect policy on the network path to the DOTS client’s domain, up to



and including instantiation of drop-lists blocking all inbound

traffic to networks for which the DOTS client is authorized to

request mitigation.

Similarly, an impersonated DOTS server may be able to act as a sort

of malicious DOTS gateway, intercepting requests from the downstream

DOTS client, and modifying them before transmission to the DOTS

server to inflict the desired impact on traffic to or from the DOTS

client’s domain. Among other things, this malicious DOTS gateway

might receive and discard mitigation requests from the DOTS client,

ensuring no requested mitigation is ever applied.

To detect misuse, as detailed in Section 2.4, DOTS implementations

require mutual authentication of DOTS agents in order to make agent

impersonation more difficult. However, impersonation may still be

possible as a result of credential theft, implementation flaws, or

compromise of DOTS agents.

To detect compromised DOTS agents, DOTS operators should carefully

monitor and audit DOTS agents to detect misbehavior and to deter

misuse, while employing current secure network communications best

practices to reduce attack surface.

Blocking communication between DOTS agents has the potential to

disrupt the core function of DOTS, which is to request mitigation of

active or expected DDoS attacks. The DOTS signal channel is expected

to operate over congested inbound links, and, as described in

Section 2.2, the signal channel protocol must be designed for minimal

data transfer to reduce the incidence of signal loss.


This document does not require any IANA action.

6. Contributors

Mohamed Boucadair

Orange

[email protected]

Flemming Andreasen

Cisco Systems, Inc.

[email protected]

Dave Dolson

Sandvine



[email protected]

7. Acknowledgments

Thanks to Roman Danyliw, Matt Richardson, Joe Touch, Scott Bradner,

Robert Sparks, Brian Weis, Benjamin Kaduk, Eric Rescorla, Alvaro

Retana, Suresh Krishnan, Ben Campbell, Mirja Kuehlewind and Jon

Shallow for careful reading and feedback.

8. References


[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,

DOI 10.17487/RFC0768, August 1980,

<https://www.rfc-editor.org/info/rfc768>.

[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,

DOI 10.17487/RFC0791, September 1981,


[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,

RFC 793, DOI 10.17487/RFC0793, September 1981,


[RFC1035] Mockapetris, P., "Domain names - implementation and

specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,

November 1987, <https://www.rfc-editor.org/info/rfc1035>.

[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -

Communication Layers", STD 3, RFC 1122,

DOI 10.17487/RFC1122, October 1989,


[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate

Requirement Levels", BCP 14, RFC 2119,

DOI 10.17487/RFC2119, March 1997,


[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform

Resource Identifier (URI): Generic Syntax", STD 66,

RFC 3986, DOI 10.17487/RFC3986, January 2005,


[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing

Architecture", RFC 4291, DOI 10.17487/RFC4291, February

2006, <https://www.rfc-editor.org/info/rfc4291>.



[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing

(CIDR): The Internet Address Assignment and Aggregation

Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August


[RFC4787] Audet, F., Ed. and C. Jennings, "Network Address

Translation (NAT) Behavioral Requirements for Unicast

UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January


[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6

Address Text Representation", RFC 5952,

DOI 10.17487/RFC5952, August 2010,


[RFC6888] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,

A., and H. Ashida, "Common Requirements for Carrier-Grade

NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888,

April 2013, <https://www.rfc-editor.org/info/rfc6888>.

[RFC7857] Penno, R., Perreault, S., Boucadair, M., Ed., Sivakumar,

S., and K. Naito, "Updates to Network Address Translation

(NAT) Behavioral Requirements", BCP 127, RFC 7857,

DOI 10.17487/RFC7857, April 2016,


[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage

Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,

March 2017, <https://www.rfc-editor.org/info/rfc8085>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC

2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,

May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6

(IPv6) Specification", STD 86, RFC 8200,

DOI 10.17487/RFC8200, July 2017,



[I-D.ietf-dots-architecture]

Mortensen, A., Andreasen, F., K, R., Teague, N., Compton,

R., and c. [email protected],

"Distributed-Denial-of-Service Open Threat Signaling

(DOTS) Architecture", draft-ietf-dots-architecture-12

(work in progress), February 2019.



[I-D.ietf-dots-use-cases]

Dobbins, R., Migault, D., Fouant, S., Moskowitz, R.,

Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS

Open Threat Signaling", draft-ietf-dots-use-cases-17 (work

in progress), January 2019.

[I-D.ietf-intarea-frag-fragile]

Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,

and F. Gont, "IP Fragmentation Considered Fragile", draft-

ietf-intarea-frag-fragile-09 (work in progress), February

2019.

[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,

A., Peterson, J., Sparks, R., Handley, M., and E.

Schooler, "SIP: Session Initiation Protocol", RFC 3261,

DOI 10.17487/RFC3261, June 2002,


[RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session

Initiation Protocol (SIP) Back-to-Back User Agents",

RFC 7092, DOI 10.17487/RFC7092, December 2013,


[RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet

Denial-of-Service Considerations", RFC 4732,

DOI 10.17487/RFC4732, December 2006,


[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",

FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,


[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,

"Recommendations for Secure Use of Transport Layer

Security (TLS) and Datagram Transport Layer Security

(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May



Andrew Mortensen

Arbor Networks

2727 S. State St

Ann Arbor, MI 48104

United States




Tirumaleswar Reddy

McAfee

Embassy Golf Link Business Park

Bangalore, Karnataka 560071

India


Robert Moskowitz

Huawei

Oak Park, MI 42837

United States



DOTS T. ReddyInternet-Draft McAfeeIntended status: Standards Track M. BoucadairExpires: December 23, 2017 Orange P. Patil Cisco A. Mortensen Arbor Networks, Inc. N. Teague Verisign, Inc. June 21, 2017

Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel draft-ietf-dots-signal-channel-02

Abstract

This document specifies the DOTS signal channel, a protocol for signaling the need for protection against Distributed Denial-of- Service (DDoS) attacks to a server capable of enabling network traffic mitigation on behalf of the requesting client. A companion document defines the DOTS data channel, a separate reliable communication layer for DOTS management and configuration.

Status of This Memo




This Internet-Draft will expire on December 23, 2017.

Copyright Notice



Internet-Draft DOTS Signal Channel June 2017


Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions and Terminology . . . . . . . . . . . 3 3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 4 4. Happy Eyeballs for DOTS Signal Channel . . . . . . . . . . . 5 5. DOTS Signal Channel . . . . . . . . . . . . . . . . . . . . . 7 5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 7 5.2. DOTS Signal YANG Model . . . . . . . . . . . . . . . . . 8 5.2.1. Mitigation Request Model structure . . . . . . . . . 8 5.2.2. Mitigation Request Model . . . . . . . . . . . . . . 8 5.2.3. Session Configuration Model structure . . . . . . . . 10 5.2.4. Session Configuration Model . . . . . . . . . . . . . 10 5.3. Mitigation Request . . . . . . . . . . . . . . . . . . . 11 5.3.1. Requesting mitigation . . . . . . . . . . . . . . . . 12 5.3.2. Withdraw a DOTS Signal . . . . . . . . . . . . . . . 17 5.3.3. Retrieving a DOTS Signal . . . . . . . . . . . . . . 18 5.3.4. Efficacy Update from DOTS Client . . . . . . . . . . 23 5.4. DOTS Signal Channel Session Configuration . . . . . . . . 25 5.4.1. Discover Acceptable Configuration Parameters . . . . 26 5.4.2. Convey DOTS Signal Channel Session Configuration . . 27 5.4.3. Delete DOTS Signal Channel Session Configuration . . 29 5.4.4. Retrieving DOTS Signal Channel Session Configuration 29 5.5. Redirected Signaling . . . . . . . . . . . . . . . . . . 30 5.6. Heartbeat Mechanism . . . . . . . . . . . . . . . . . . . 31 6. Mapping parameters to CBOR . . . . . . . . . . . . . . . . . 32 7. (D)TLS Protocol Profile and Performance considerations . . . 32 7.1. MTU and Fragmentation Issues . . . . . . . . . . . . . . 33 8. (D)TLS 1.3 considerations . . . . . . . . . . . . . . . . . . 34 9. Mutual Authentication of DOTS Agents & Authorization of DOTS Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37 10.1. DOTS signal channel CBOR Mappings Registry . . . . . . . 37 10.1.1. Registration Template . . . . . . . . . . . . . . . 37 10.1.2. Initial Registry Contents . . . . . . . . . . . . . 37 11. Implementation Status . . . . . . . . . . . . . . . . . . . . 41 11.1. nttdots . . . . . . . . . . . . . . . . . . . . . . . . 41 12. Security Considerations . . . . . . . . . . . . . . . . . . . 42



13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 42 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 43 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 43 15.1. Normative References . . . . . . . . . . . . . . . . . . 43 15.2. Informative References . . . . . . . . . . . . . . . . . 44 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 46

1. Introduction

A distributed denial-of-service (DDoS) attack is an attempt to make machines or network resources unavailable to their intended users. In most cases, sufficient scale can be achieved by compromising enough end-hosts and using those infected hosts to perpetrate and amplify the attack. The victim in this attack can be an application server, a host, a router, a firewall, or an entire network.

In many cases, it may not be possible for an network administrators to determine the causes of an attack, but instead just realize that certain resources seem to be under attack. This document defines a lightweight protocol permitting a DOTS client to request mitigation from one or more DOTS servers for protection against detected, suspected, or anticipated attacks . This protocol enables cooperation between DOTS agents to permit a highly-automated network defense that is robust, reliable and secure.

The requirements for DOTS signal channel protocol are obtained from [I-D.ietf-dots-requirements].

This document satisfies all the use cases discussed in [I-D.ietf-dots-use-cases] except the Third-party DOTS notifications use case in Section 3.2.3 of [I-D.ietf-dots-use-cases] which is an optional feature and not a core use case. Third-party DOTS notifications are not part of the DOTS requirements document. Moreover, the DOTS architecture does not assess whether that use case may have an impact on the architecture itself and/or the DOTS trust model.

This is a companion document to the DOTS data channel specification [I-D.ietf-dots-data-channel] that defines a configuration and bulk data exchange mechanism supporting the DOTS signal channel.

2. Notational Conventions and Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].



(D)TLS: For brevity this term is used for statements that apply to both Transport Layer Security [RFC5246] and Datagram Transport Layer Security [RFC6347]. Specific terms will be used for any statement that applies to either protocol alone.

The reader should be familiar with the terms defined in [I-D.ietf-dots-architecture].

3. Solution Overview

Network applications have finite resources like CPU cycles, number of processes or threads they can create and use, maximum number of simultaneous connections it can handle, limited resources of the control plane, etc. When processing network traffic, such applications are supposed to use these resources to offer the intended task in the most efficient fashion. However, an attacker may be able to prevent an application from performing its intended task by causing the application to exhaust the finite supply of a specific resource.

TCP DDoS SYN-flood, for example, is a memory-exhaustion attack on the victim and ACK-flood is a CPU exhaustion attack on the victim ([RFC4987]). Attacks on the link are carried out by sending enough traffic such that the link becomes excessively congested, and legitimate traffic suffers high packet loss. Stateful firewalls can also be attacked by sending traffic that causes the firewall to hold excessive state. The firewall then runs out of memory, and can no longer instantiate the state required to pass legitimate flows. Other possible DDoS attacks are discussed in [RFC4732].

In each of the cases described above, the possible arrangements between the DOTS client and DOTS server to mitigate the attack are discussed in [I-D.ietf-dots-use-cases]. An example of network diagram showing a deployment of these elements is shown in Figure 1. Architectural relationships between involved DOTS agents is explained in [I-D.ietf-dots-architecture]. In this example, the DOTS server is operating on the access network.

Network Resource CPE router Access network __________ +-----------+ +--------------+ +-------------+ / \ | |____| |_______| |___ | Internet | |DOTS client| | DOTS gateway | | DOTS server | | | | | | | | | | | +-----------+ +--------------+ +-------------+ \__________/

Figure 1: Sample DOTS Deployment (1)



The DOTS server can also be running on the Internet, as depicted in Figure 2.

Network DDoS mitigation Resource CPE router __________ service +-----------+ +-------------+ / \ +-------------+ | |____| |_______| |___ | | |DOTS client| |DOTS gateway | | Internet | | DOTS server | | | | | | | | | | +-----------+ +-------------+ \__________/ +-------------+


In typical deployments, the DOTS client belongs to a different administrative domain than the DOTS server. For example, the DOTS client is a firewall protecting services owned and operated by an domain, while the DOTS server is owned and operated by a different domain providing DDoS mitigation services. That domain providing DDoS mitigation service might, or might not, also provide Internet access service to the website operator.

The DOTS server may (not) be co-located with the DOTS mitigator. In typical deployments, the DOTS server belongs to the same administrative domain as the mitigator.

The DOTS client can communicate directly with the DOTS server or indirectly via a DOTS gateway.

This document focuses on the DOTS signal channel.

4. Happy Eyeballs for DOTS Signal Channel

DOTS signaling can happen with DTLS [RFC6347] over UDP and TLS [RFC5246] over TCP. A DOTS client can use DNS to determine the IP address(es) of a DOTS server or a DOTS client may be provided with the list of DOTS server IP addresses. The DOTS client MUST know a DOTS server’s domain name; hard-coding the domain name of the DOTS server into software is NOT RECOMMENDED in case the domain name is not valid or needs to change for legal or other reasons. The DOTS client performs A and/or AAAA record lookup of the domain name and the result will be a list of IP addresses, each of which can be used to contact the DOTS server using UDP and TCP.

If an IPv4 path to reach a DOTS server is found, but the DOTS server’s IPv6 path is not working, a dual-stack DOTS client can experience a significant connection delay compared to an IPv4-only DOTS client. The other problem is that if a middlebox between the DOTS client and DOTS server is configured to block UDP, the DOTS



client will fail to establish a DTLS session with the DOTS server and will, then, have to fall back to TLS over TCP incurring significant connection delays. [I-D.ietf-dots-requirements] discusses that DOTS client and server will have to support both connectionless and connection-oriented protocols.

To overcome these connection setup problems, the DOTS client can try connecting to the DOTS server using both IPv6 and IPv4, and try both DTLS over UDP and TLS over TCP in a fashion similar to the Happy Eyeballs mechanism [RFC6555]. These connection attempts are performed by the DOTS client when its initializes, and the client uses that information for its subsequent alert to the DOTS server. In order of preference (most preferred first), it is UDP over IPv6, UDP over IPv4, TCP over IPv6, and finally TCP over IPv4, which adheres to address preference order [RFC6724] and the DOTS preference that UDP be used over TCP (to avoid TCP’s head of line blocking).

DOTS client DOTS server | | |--DTLS ClientHello, IPv6 ---->X | |--TCP SYN, IPv6-------------->X | |--DTLS ClientHello, IPv4 ---->X | |--TCP SYN, IPv4----------------------------------------->| |--DTLS ClientHello, IPv6 ---->X | |--TCP SYN, IPv6-------------->X | |<-TCP SYNACK---------------------------------------------| |--DTLS ClientHello, IPv4 ---->X | |--TCP ACK----------------------------------------------->| |<------------Establish TLS Session---------------------->| |----------------DOTS signal----------------------------->| | |

Figure 3: Happy Eyeballs

In reference to Figure 3, the DOTS client sends two TCP SYNs and two DTLS ClientHello messages at the same time over IPv6 and IPv4. In this example, it is assumed that the IPv6 path is broken and UDP is dropped by a middle box but has little impact to the DOTS client because there is no long delay before using IPv4 and TCP. The DOTS client repeats the mechanism to discover if DOTS signaling with DTLS over UDP becomes available from the DOTS server, so the DOTS client can migrate the DOTS signal channel from TCP to UDP, but such probing SHOULD NOT be done more frequently than every 24 hours and MUST NOT be done more frequently than every 5 minutes.



5. DOTS Signal Channel

5.1. Overview

The DOTS signal channel is built on top of the Constrained Application Protocol (CoAP) [RFC7252], a lightweight protocol originally designed for constrained devices and networks. CoAP’s expectation of packet loss, support for asynchronous non-confirmable messaging, congestion control, small message overhead limiting the need for fragmentation, use of minimal resources, and support for (D)TLS make it a good foundation on which to build the DOTS signaling mechanism.

The DOTS signal channel is layered on existing standards (Figure 4).

+--------------+ | DOTS | +--------------+ | CoAP | +--------------+ | TLS | DTLS | +--------------+ | TCP | UDP | +--------------+ | IP | +--------------+

Figure 4: Abstract Layering of DOTS signal channel over CoAP over (D)TLS

The signal channel is initiated by the DOTS client. Once the signal channel is established, the DOTS agents periodically send heartbeats to keep the channel active. At any time, the DOTS client may send a mitigation request message to the DOTS server over the active channel. While mitigation is active, the DOTS server periodically sends status messages to the client, including basic mitigation feedback details. Mitigation remains active until the DOTS client explicitly terminates mitigation, or the mitigation lifetime expires.

Messages exchanged between DOTS client and server are serialized using Concise Binary Object Representation (CBOR) [RFC7049], CBOR is a binary encoding designed for small code and message size. CBOR encoded payloads are used to convey signal channel specific payload messages that convey request parameters and response information such as errors. This specification uses the encoding rules defined in [I-D.ietf-core-yang-cbor] for representing mitigation scope and DOTS signal channel session configuration data defined using YANG (Section 5.2) as CBOR data.



5.2. DOTS Signal YANG Model

This document defines a YANG [RFC6020] data model for mitigation scope and DOTS signal channel session configuration data.

5.2.1. Mitigation Request Model structure

This document defines the YANG module "ietf-dots-signal", which has the following structure:

module: ietf-dots-signal +--rw mitigation-scope +--rw scope* [mitigation-id] +--rw mitigation-id int32 +--rw target-ip* inet:ip-address +--rw target-prefix* inet:ip-prefix +--rw target-port-range* [lower-port upper-port] | +--rw lower-port inet:port-number | +--rw upper-port inet:port-number +--rw target-protocol* uint8 +--rw fqdn* inet:domain-name +--rw uri* inet:uri +--rw alias* string +--rw lifetime? int32

5.2.2. Mitigation Request Model


module ietf-dots-signal { namespace "urn:ietf:params:xml:ns:yang:ietf-dots-signal"; prefix "signal"; import ietf-inet-types { prefix "inet"; } organization "McAfee, Inc."; contact "Konda, Tirumaleswar Reddy <[email protected]>";

description "This module contains YANG definition for DOTS signal sent by the DOTS client to the DOTS server";

revision 2016-11-28 { reference "https://tools.ietf.org/html/draft-reddy-dots-signal-channel"; }

container mitigation-scope {



description "top level container for mitigation request"; list scope { key mitigation-id; description "Identifier for the mitigation request"; leaf mitigation-id { type int32; description "mitigation request identifier"; } leaf-list target-ip { type inet:ip-address; description "IP address"; } leaf-list target-prefix { type inet:ip-prefix; description "prefix"; } list target-port-range { key "lower-port upper-port"; description "Port range. When only lower-port is present, it represents a single port."; leaf lower-port { type inet:port-number; mandatory true; description "lower port"; } leaf upper-port { type inet:port-number; must ". >= ../lower-port" { error-message "The upper-port must be greater than or equal to lower-port"; } description "upper port"; } } leaf-list target-protocol { type uint8; description "Internet Protocol number"; } leaf-list fqdn { type inet:domain-name; description "FQDN"; } leaf-list uri { type inet:uri; description "URI"; } leaf-list alias {



type string; description "alias name"; } leaf lifetime { type int32; description "lifetime"; } } } }<CODE ENDS>

5.2.3. Session Configuration Model structure

This document defines the YANG module "ietf-dots-signal-config", which has the following structure:

module: ietf-dots-signal-config +--rw signal-config +--rw session-id? int32 +--rw heartbeat-timeout? int16 +--rw max-retransmit? int16 +--rw ack-timeout? int16 +--rw ack-random-factor? decimal64

5.2.4. Session Configuration Model


module ietf-dots-signal-config { namespace "urn:ietf:params:xml:ns:yang:ietf-dots-signal-config"; prefix "config";

organization "McAfee, Inc."; contact "Konda, Tirumaleswar Reddy <[email protected]>";

description "This module contains YANG definition for DOTS signal channel session configuration";

revision 2016-11-28 { reference "https://tools.ietf.org/html/draft-reddy-dots-signal-channel"; }

container signal-config { description "top level container for DOTS signal channel session configuration";



leaf session-id { type int32; description "Identifier for the DOTS signal channel session configuration data"; } leaf heartbeat-timeout { type int16; description "heartbeat timeout"; } leaf max-retransmit { type int16; description "Maximum number of retransmissions"; } leaf ack-timeout { type int16; description "Initial retransmission timeout value"; } leaf ack-random-factor { type decimal64 { fraction-digits 2; } description "Random factor used to influence the timing of retransmissions"; } }}

<CODE ENDS>

5.3. Mitigation Request

The following methods are used to request or withdraw mitigation requests:

PUT: DOTS clients use the PUT method to request mitigation (Section 5.3.1). During active mitigation, DOTS clients may use PUT requests to convey mitigation efficacy updates to the DOTS server (Section 5.3.4).

DELETE: DOTS clients use the DELETE method to withdraw a request for mitigation from the DOTS server (Section 5.3.2).

GET: DOTS clients may use the GET method to subscribe to DOTS server status messages, or to retrieve the list of existing mitigations (Section 5.3.3).

Mitigation request and response messages are marked as Non- confirmable messages. DOTS agents should follow the data



transmission guidelines discussed in Section 3.1.3 of [RFC8085] and control transmission behavior by not sending on average more than one UDP datagram per RTT to the peer DOTS agent. Requests marked by the DOTS client as Non-confirmable messages are sent at regular intervals until a response is received from the DOTS server and if the DOTS client cannot maintain a RTT estimate then it SHOULD NOT send more than one Non-confirmable request every 3 seconds, and SHOULD use an even less aggressive rate when possible (case 2 in Section 3.1.3 of [RFC8085]).

5.3.1. Requesting mitigation

When a DOTS client requires mitigation for any reason, the DOTS client uses CoAP PUT method to send a mitigation request to the DOTS server (Figure 5, illustrated in JSON diagnostic notation). The DOTS server can enable mitigation on behalf of the DOTS client by communicating the DOTS client’s request to the mitigator and relaying selected mitigator feedback to the requesting DOTS client.



Header: PUT (Code=0.03) Uri-Host: "host" Uri-Path: "version" Uri-Path: "dots-signal" Uri-Path: "signal" Content-Type: "application/cbor" { "mitigation-scope": { "scope": [ { "mitigation-id": integer, "target-ip": [ "string" ], "target-prefix": [ "string" ], "target-port-range": [ { "lower-port": integer, "upper-port": integer } ], "target-protocol": [ integer ], "fqdn": [ "string" ], "uri": [ "string" ], "alias": [ "string" ], "lifetime": integer } ] } }

Figure 5: PUT to convey DOTS signals

The parameters are described below.

mitigation-id: Identifier for the mitigation request represented using an integer. This identifier MUST be unique for each mitigation request bound to the DOTS client, i.e., the mitigation-



id parameter value in the mitigation request needs to be unique relative to the mitigation-id parameter values of active mitigation requests conveyed from the DOTS client to the DOTS server. This identifier MUST be generated by the DOTS client. This document does not make any assumption about how this identifier is generated. This is a mandatory attribute.

target-ip: A list of IP addresses under attack. This is an optional attribute.

target-prefix: A list of prefixes under attack. Prefixes are represented using CIDR notation [RFC4632]. This is an optional attribute.

target-port-range: A list of ports under attack. The port range, lower-port for lower port number and upper-port for upper port number. When only lower-port is present, it represents a single port. For TCP, UDP, SCTP, or DCCP: the range of ports (e.g., 1024-65535). This is an optional attribute.

target-protocol: A list of protocols under attack. Internet Protocol numbers. This is an optional attribute.

fqdn: A list of Fully Qualified Domain Names. Fully Qualified Domain Name (FQDN) is the full name of a system, rather than just its hostname. For example, "venera" is a hostname, and "venera.isi.edu" is an FQDN. This is an optional attribute.

uri: A list of Uniform Resource Identifiers (URI). This is an optional attribute.

alias: A list of aliases. Aliases can be created using the DOTS data channel (Section 3.1.1 in [I-D.ietf-dots-data-channel]) or direct configuration , or other means and then used in subsequent signal channel exchanges to refer more efficiently to the resources under attack. This is an optional attribute.

lifetime: Lifetime of the mitigation request in seconds. Upon the expiry of this lifetime, and if the request is not refreshed, the mitigation request is removed. The request can be refreshed by sending the same request again. The default lifetime of the mitigation request is 3600 seconds (60 minutes) -- this value was chosen to be long enough so that refreshing is not typically a burden on the DOTS client, while expiring the request where the client has unexpectedly quit in a timely manner. A lifetime of zero indicates indefinite lifetime for the mitigation request. The server MUST always indicate the actual lifetime in the



response and the remaining lifetime in status messages sent to the client. This is an optional attribute in the request.

The CBOR key values for the parameters are defined in Section 6. The IANA Considerations section defines how the CBOR key values can be allocated to standards bodies and vendors. In the PUT request at least one of the attributes target-ip or target-prefix or fqdn or uri or alias MUST be present. DOTS agents can safely ignore Vendor- Specific parameters they don’t understand. The relative order of two mitigation requests from a DOTS client is determined by comparing their respective mitigation-id values. If two mitigation requests have overlapping mitigation scopes the mitigation request with higher numeric mitigation-id value will override the mitigation request with a lower numeric mitigation-id value. The Uri-Path option carries a major and minor version nomenclature to manage versioning and DOTS signal channel in this specification uses v1 major version.

In both DOTS signal and data channel sessions, the DOTS client MUST authenticate itself to the DOTS server (Section 9). The DOTS server can use the algorithm discussed in Section 7 of [RFC7589] to derive the DOTS client identity or username from the client certificate. The DOTS server couples the DOTS signal and data channel sessions using the DOTS client identity, so the DOTS server can validate whether the aliases conveyed in the mitigation request were indeed created by the same DOTS client using the DOTS data channel session. If the aliases were not created by the DOTS client then the DOTS server returns 4.00 (Bad Request) in the response. The DOTS server couples the DOTS signal channel sessions using the DOTS client identity, and the DOTS server uses mitigation-id parameter value to detect duplicate mitigation requests.

Figure 6 shows a PUT request example to signal that ports 80, 8080, and 443 on the servers 2001:db8:6401::1 and 2001:db8:6401::2 are being attacked (illustrated in JSON diagnostic notation).

Header: PUT (Code=0.03) Uri-Host: "www.example.com" Uri-Path: "v1" Uri-Path: "dots-signal" Uri-Path: "signal" Content-Format: "application/cbor" { "mitigation-scope": { "scope": [ { "mitigation-id": 12332, "target-ip": [ "2001:db8:6401::1",



"2001:db8:6401::2" ], "target-port-range": [ { "lower-port": 80 }, { "lower-port": 443 }, { "lower-port": 8080 } ], "target-protocol": [ 6 ] } ] } }

The CBOR encoding format is shown below:

a1 # map(1) 01 # unsigned(1) a1 # map(1) 02 # unsigned(2) 81 # array(1) a4 # map(4) 03 # unsigned(3) 19 302c # unsigned(12332) 04 # unsigned(4) 82 # array(2) 70 # text(16) 323030313A6462383A363430313A3A31 # "2001:db8:6401::1" 70 # text(16) 323030313A6462383A363430313A3A32 # "2001:db8:6401::2" 05 # unsigned(5) 83 # array(3) a1 # map(1) 06 # unsigned(6) 18 50 # unsigned(80) a1 # map(1) 06 # unsigned(6) 19 01bb # unsigned(443) a1 # map(1) 06 # unsigned(6) 19 1f90 # unsigned(8080)



08 # unsigned(8) 81 # array(1) 06 # unsigned(6)

Figure 6: POST for DOTS signal

The DOTS server indicates the result of processing the PUT request using CoAP response codes. CoAP 2.xx codes are success. CoAP 4.xx codes are some sort of invalid requests. COAP 5.xx codes are returned if the DOTS server has erred or is currently unavailable to provide mitigation in response to the mitigation request from the DOTS client. If the DOTS server does not find the mitigation-id parameter value conveyed in the PUT request in its configuration data then the server MAY accept the mitigation request, and a 2.01 (Created) response is returned to the DOTS client, and the DOTS server will try to mitigate the attack. If the DOTS server finds the mitigation-id parameter value conveyed in the PUT request in its configuration data then the server MAY update the mitigation request, and a 2.04 (Changed) response is returned to indicate a successful update of the mitigation request. If the request is missing one or more mandatory attributes, then 4.00 (Bad Request) will be returned in the response or if the request contains invalid or unknown parameters then 4.02 (Invalid query) will be returned in the response. For responses indicating a client or server error, the payload explains the error situation of the result of the requested action (Section 5.5 in [RFC7252]).

5.3.2. Withdraw a DOTS Signal

A DELETE request is used to withdraw a DOTS signal from a DOTS server (Figure 7).



Header: DELETE (Code=0.04) Uri-Host: "host" Uri-Path: "version" Uri-Path: "dots-signal" Uri-Path: "signal" Content-Format: "application/cbor" { "mitigation-scope": { "scope": [ { "mitigation-id": integer } ] } }

Figure 7: Withdraw DOTS signal

If the DOTS server does not find the mitigation-id parameter value conveyed in the DELETE request in its configuration data, then it responds with a 4.04 (Not Found) error response code. The DOTS server successfully acknowledges a DOTS client’s request to withdraw the DOTS signal using 2.02 (Deleted) response code, and ceases mitigation activity as quickly as possible.

To protect against route or DNS flapping caused by a client rapidly toggling mitigation, and to dampen the effect of oscillating attacks, DOTS servers MAY continue mitigation for a period of up to five minutes after acknowledging a DOTS client’s withdrawal of a mitigation request. During this period, DOTS server status messages SHOULD indicate that mitigation is active but terminating. After the five-minute period elapses, the DOTS server MUST treat the mitigation as terminated, as the DOTS client is no longer responsible for the mitigation. For example, if there is a financial relationship between the DOTS client and server domains, the DOTS client ceases incurring cost at this point.

5.3.3. Retrieving a DOTS Signal

A GET request is used to retrieve information and status of a DOTS signal from a DOTS server (Figure 8). If the DOTS server does not find the mitigation-id parameter value conveyed in the GET request in its configuration data, then it responds with a 4.04 (Not Found) error response code. The ’c’ (content) parameter and its permitted values defined in [I-D.ietf-core-comi] can be used to retrieve non- configuration data or configuration data or both.



1) To retrieve all DOTS signals signaled by the DOTS client.

Header: GET (Code=0.01) Uri-Host: "host" Uri-Path: "version" Uri-Path: "dots-signal" Uri-Path: "signal" Observe : 0

2) To retrieve a specific DOTS signal signaled by the DOTS client. The configuration data in the response will be formatted in the same order it was processed at the DOTS server.

Header: GET (Code=0.01) Uri-Host: "host" Uri-Path: "version" Uri-Path: "dots-signal" Uri-Path: "signal" Observe : 0 Content-Format: "application/cbor" { "mitigation-scope": { "scope": [ { "mitigation-id": integer } ] } }

Figure 8: GET to retrieve the rules

Figure 9 shows a response example of all the active mitigation requests associated with the DOTS client on the DOTS server and the mitigation status of each mitigation request.



{ "mitigation-scope":[ { "scope": [ { "mitigation-id": 12332, "target-protocol": [ 17 ], "lifetime":1800, "status":2, "bytes-dropped": 134334555, "bps-dropped": 43344, "pkts-dropped": 333334444, "pps-dropped": 432432 } ] }, { "scope": [ { "mitigation-id": 12333, "target-protocol": [ 6 ], "lifetime":1800, "status":3 "bytes-dropped": 0, "bps-dropped": 0, "pkts-dropped": 0, "pps-dropped": 0 } ] } ] }

Figure 9: Response body

The mitigation status parameters are described below.

bytes-dropped: The total dropped byte count for the mitigation request. This is a optional attribute.

bps-dropped: The average dropped bytes per second for the mitigation request. This is a optional attribute.



pkts-dropped: The total dropped packet count for the mitigation request. This is a optional attribute.

pps-dropped: The average dropped packets per second for the mitigation request. This is a optional attribute.

status: Status of attack mitigation. The ’status’ parameter is a mandatory attribute.

The various possible values of ’status’ parameter are explained below:

/--------------------+---------------------------------------------------\| Parameter value | Description ||--------------------+---------------------------------------------------|| 1 | Attack mitigation is in progress || | (e.g., changing the network path to re-route the || | inbound traffic to DOTS mitigator). |+------------------------------------------------------------------------+| 2 | Attack is successfully mitigated || | (e.g., traffic is redirected to a DDOS mitigator || | and attack traffic is dropped). |+------------------------------------------------------------------------+| 3 | Attack has stopped and the DOTS client || | can withdraw the mitigation request. |+------------------------------------------------------------------------+| 4 | Attack has exceeded the mitigation provider || | capability. |+------------------------------------------------------------------------+| 5 | DOTS client has withdrawn the mitigation request | and the mitigation is active but terminating. || | |\--------------------+---------------------------------------------------/

The observe option defined in [RFC7641] extends the CoAP core protocol with a mechanism for a CoAP client to "observe" a resource on a CoAP server: the client retrieves a representation of the resource and requests this representation be updated by the server as long as the client is interested in the resource. A DOTS client conveys the observe option set to 0 in the GET request to receive unsolicited notifications of attack mitigation status from the DOTS server. Unidirectional notifications within the bidirectional signal channel allows unsolicited message delivery, enabling asynchronous notifications between the agents. A DOTS client that is no longer interested in receiving notifications from the DOTS server can simply "forget" the observation. When the DOTS server then sends the next notification, the DOTS client will not recognize the token in the



message and thus will return a Reset message. This causes the DOTS server to remove the associated entry.

DOTS Client DOTS Server | | | GET /<mitigation-id number> | | Token: 0x4a | Registration | Observe: 0 | +------------------------------>| | | | 2.05 Content | | Token: 0x4a | Notification of | Observe: 12 | the current state | status: "mitigation | | in progress" | |<------------------------------+ | 2.05 Content | | Token: 0x4a | Notification upon | Observe: 44 | a state change | status: "mitigation | | complete" | |<------------------------------+ | 2.05 Content | | Token: 0x4a | Notification upon | Observe: 60 | a state change | status: "attack stopped" | |<------------------------------+ | |

Figure 10: Notifications of attack mitigation status

5.3.3.1. Mitigation Status

A DOTS client retrieves the information about a DOTS signal at frequent intervals to determine the status of an attack. If the DOTS server has been able to mitigate the attack and the attack has stopped, the DOTS server indicates as such in the status, and the DOTS client recalls the mitigation request.

A DOTS client should react to the status of the attack from the DOTS server and not the fact that it has recognized, using its own means, that the attack has been mitigated. This ensures that the DOTS client does not recall a mitigation request in a premature fashion because it is possible that the DOTS client does not sense the DDOS attack on its resources but the DOTS server could be actively mitigating the attack and the attack is not completely averted.



5.3.4. Efficacy Update from DOTS Client

While DDoS mitigation is active, a DOTS client MAY frequently transmit DOTS mitigation efficacy updates to the relevant DOTS server. An PUT request (Figure 11) is used to convey the mitigation efficacy update to the DOTS server. The PUT request MUST include all the parameters used in the PUT request to convey the DOTS signal (Section 5.3.1).



Header: PUT (Code=0.03) Uri-Host: "host" Uri-Path: "version" Uri-Path: "dots-signal" Uri-Path: "signal" Content-Format: "application/cbor" { "mitigation-scope": { "scope": [ { "mitigation-id": integer, "target-ip": [ "string" ], "target-port-range": [ { "lower-port": integer, "upper-port": integer } ], "target-protocol": [ integer ], "fqdn": [ "string" ], "uri": [ "string" ], "alias": [ "string" ], "lifetime": integer, "attack-status": integer } ] } }

Figure 11: Efficacy Update

The ’attack-status’ parameter is a mandatory attribute. The various possible values contained in the ’attack-status’ parameter are explained below:



/--------------------+------------------------------------------------------\| Parameter value | Description ||--------------------+------------------------------------------------------|| 1 | DOTS client determines that it is still under attack.|+---------------------------------------------------------------------------+| 2 | DOTS client determines that the attack is || | successfully mitigated || | (e.g., attack traffic is not seen). |\--------------------+------------------------------------------------------/

The DOTS server indicates the result of processing the PUT request using CoAP response codes. The response code 2.04 (Changed) will be returned in the response if the DOTS server has accepted the mitigation efficacy update. If the DOTS server does not find the mitigation-id parameter value conveyed in the PUT request in its configuration data then the server MAY accept the mitigation request and will try to mitigate the attack, resulting in a 2.01 (Created) Response Code. The 5.xx response codes are returned if the DOTS server has erred or is incapable of performing the mitigation.

5.4. DOTS Signal Channel Session Configuration

The DOTS client can negotiate, configure and retrieve the DOTS signal channel session behavior. The DOTS signal channel can be used, for example, to configure the following:

a. Heartbeat timeout: DOTS agents regularly send heartbeats (Ping/ Pong) to each other after mutual authentication in order to keep the DOTS signal channel open, heartbeat timeout is the time to wait for a Pong in milliseconds.

b. Acceptable signal loss ratio: Maximum retransmissions, retransmission timeout value and other message transmission parameters for the DOTS signal channel.

Reliability is provided to requests and responses by marking them as Confirmable (CON) messages. DOTS signal channel session configuration requests and responses are marked as Confirmable (CON) messages. As explained in Section 2.1 of [RFC7252], a Confirmable message is retransmitted using a default timeout and exponential back-off between retransmissions, until the DOTS server sends an Acknowledgement message (ACK) with the same Message ID conveyed from the DOTS client. Message transmission parameters are defined in Section 4.8 of [RFC7252]. Reliability is provided to the responses by marking them as Confirmable (CON) messages. The DOTS server can either piggyback the response in the acknowledgement message or if the DOTS server is not able to respond immediately to a request



carried in a Confirmable message, it simply responds with an Empty Acknowledgement message so that the DOTS client can stop retransmitting the request. Empty Acknowledgement message is explained in Section 2.2 of [RFC7252]. When the response is ready, the server sends it in a new Confirmable message which then in turn needs to be acknowledged by the DOTS client (see Sections 5.2.1 and Sections 5.2.2 in [RFC7252]). Requests and responses exchanged between DOTS agents during peacetime are marked as Confirmable messages.

Implementation Note: A DOTS client that receives a response in a CON message may want to clean up the message state right after sending the ACK. If that ACK is lost and the DOTS server retransmits the CON, the DOTS client may no longer have any state to which to correlate this response, making the retransmission an unexpected message; the DOTS client will send a Reset message so it does not receive any more retransmissions. This behavior is normal and not an indication of an error (see Section 5.3.2 in [RFC7252] for more details).

5.4.1. Discover Acceptable Configuration Parameters

A GET request is used to obtain acceptable configuration parameters on the DOTS server for DOTS signal channel session configuration. Figure 12 shows how to obtain acceptable configuration parameters for the server.

Header: GET (Code=0.01) Uri-Host: "host" Uri-Path: "version" Uri-Path: "dots-signal" Uri-Path: "config"

Figure 12: GET to retrieve configuration

The DOTS server in the 2.05 (Content) response conveys the minimum and maximum attribute values acceptable by the DOTS server.

Content-Format: "application/cbor" { "heartbeat-timeout": {"MinValue": integer, "MaxValue" : integer}, "max-retransmit": {"MinValue": integer, "MaxValue" : integer}, "ack-timeout": {"MinValue": integer, "MaxValue" : integer}, "ack-random-factor": {"MinValue": number, "MaxValue" : number} }

Figure 13: GET response body



5.4.2. Convey DOTS Signal Channel Session Configuration

A POST request is used to convey the configuration parameters for the signaling channel (e.g., heartbeat timeout, maximum retransmissions etc). Message transmission parameters for CoAP are defined in Section 4.8 of [RFC7252]. If the DOTS agent wishes to change the default values of message transmission parameters then it should follow the guidance given in Section 4.8.1 of [RFC7252]. The DOTS agents MUST use the negotiated values for message transmission parameters and default values for non-negotiated message transmission parameters. The signaling channel session configuration is applicable to a single DOTS signal channel session between the DOTS agents.

Header: POST (Code=0.02) Uri-Host: "host" Uri-Path: "version" Uri-Path: "dots-signal" Uri-Path: "config" Content-Format: "application/cbor" { "signal-config": { "session-id": integer, "heartbeat-timeout": integer, "max-retransmit": integer, "ack-timeout": integer, "ack-random-factor": number } }

Figure 14: POST to convey the DOTS signal channel session configuration data.


session-id: Identifier for the DOTS signal channel session configuration data represented as an integer. This identifier MUST be generated by the DOTS client. This document does not make any assumption about how this identifier is generated. This is a mandatory attribute.

heartbeat-timeout: Heartbeat timeout is the time to wait for a response in milliseconds to check the DOTS peer health. This is an optional attribute.

max-retransmit: Maximum number of retransmissions for a message (referred to as MAX_RETRANSMIT parameter in CoAP). This is an optional attribute.



ack-timeout: Timeout value in seconds used to calculate the initial retransmission timeout value (referred to as ACK_TIMEOUT parameter in CoAP). This is an optional attribute.

ack-random-factor: Random factor used to influence the timing of retransmissions (referred to as ACK_RANDOM_FACTOR parameter in CoAP). This is an optional attribute.

In the POST request at least one of the attributes heartbeat-timeout or max-retransmit or ack-timeout or ack-random-factor MUST be present. The POST request with higher numeric session-id value overrides the DOTS signal channel session configuration data installed by a POST request with a lower numeric session-id value.

Figure 15 shows a POST request example to convey the configuration parameters for the DOTS signal channel.

Header: POST (Code=0.02) Uri-Host: "www.example.com" Uri-Path: "v1" Uri-Path: "dots-signal" Uri-Path: "config" Content-Format: "application/cbor" { "signal-config": { "session-id": 1234534333242, "heartbeat-timeout": 30, "max-retransmit": 7, "ack-timeout": 5, "ack-random-factor": 1.5 } }

Figure 15: POST to convey the configuration parameters

The DOTS server indicates the result of processing the POST request using CoAP response codes. The CoAP response will include the CBOR body received in the request. Response code 2.01 (Created) will be returned in the response if the DOTS server has accepted the configuration parameters. If the request is missing one or more mandatory attributes then 4.00 (Bad Request) will be returned in the response or if the request contains invalid or unknown parameters then 4.02 (Invalid query) will be returned in the response. Response code 4.22 (Unprocessable Entity) will be returned in the response if any of the heartbeat-timeout, max-retransmit, target-protocol, ack- timeout and ack-random-factor attribute values is not acceptable to the DOTS server. The DOTS server in the error response conveys the minimum and maximum attribute values acceptable by the DOTS server.



The DOTS client can re-try and send the POST request with updated attribute values acceptable to the DOTS server.

Content-Format: "application/cbor" { "heartbeat-timeout": {"MinValue": 15, "MaxValue" : 60}, "max-retransmit": {"MinValue": 3, "MaxValue" : 15}, "ack-timeout": {"MinValue": 1, "MaxValue" : 30}, "ack-random-factor": {"MinValue": 1.0, "MaxValue" : 4.0} }

Figure 16: Error response body

5.4.3. Delete DOTS Signal Channel Session Configuration

A DELETE request is used to delete the installed DOTS signal channel session configuration data (Figure 17).

Header: DELETE (Code=0.04) Uri-Host: "host" Uri-Path: "version" Uri-Path: "dots-signal" Uri-Path: "config" Content-Format: "application/cbor" { "signal-config": { "session-id": integer } }

Figure 17: DELETE configuration

If the DOTS server does not find the session-id parameter value conveyed in the DELETE request in its configuration data, then it responds with a 4.04 (Not Found) error response code. The DOTS server successfully acknowledges a DOTS client’s request to remove the DOTS signal channel session configuration using 2.02 (Deleted) response code.

5.4.4. Retrieving DOTS Signal Channel Session Configuration

A GET request is used to retrieve the installed DOTS signal channel session configuration data from a DOTS server. Figure 18 shows how to retrieve the DOTS signal channel session configuration data.



Header: GET (Code=0.01) Uri-Host: "host" Uri-Path: "version" Uri-Path: "dots-signal" Uri-Path: "config" Content-Format: "application/cbor" { "signal-config": { "session-id": integer } }

Figure 18: GET to retrieve configuration

5.5. Redirected Signaling

Redirected Signaling is discussed in detail in Section 3.2.2 of [I-D.ietf-dots-architecture]. If the DOTS server wants to redirect the DOTS client to an alternative DOTS server for a signaling session then the response code 3.00 (alternate server) will be returned in the response to the client. The DOTS server can return the error response code 3.00 in response to a POST or PUT request from the DOTS client or convey the error response code 3.00 in a unidirectional notification response from the DOTS server.

The DOTS server in the error response conveys the alternate DOTS server FQDN, and the alternate DOTS server IP addresses and time to live values in the CBOR body.

{ "alt-server": "string", "alt-server-record": [ { "addr": "string", "ttl" : integer, } ] }

Figure 19: Error response body


alt-server: FQDN of alternate DOTS server.

addr: IP address of alternate DOTS server.

ttl: Time to live (TTL) represented as an integer number of seconds.



Figure 20 shows a 3.00 response example to convey the DOTS alternate server www.example-alt.com, its IP addresses 2001:db8:6401::1 and 2001:db8:6401::2, and TTL values 3600 and 1800.

{

"alt-server": "www.example-alt.com", "alt-server-record": [ { "ttl" : 3600, "addr": "2001:db8:6401::1" }, { "ttl" : 1800, "addr": "2001:db8:6401::2" } ] }

Figure 20: Example of error response body

When the DOTS client receives 3.00 response, it considers the current request as having failed, but SHOULD try the request with the alternate DOTS server. During a DDOS attack, the DNS server may be subjected to DDOS attack, alternate DOTS server IP addresses conveyed in the 3.00 response help the DOTS client to skip DNS lookup of the alternate DOTS server and can try to establish UDP or TCP session with the alternate DOTS server IP addresses. The DOTS client SHOULD implement DNS64 function to handle the scenario where IPv6-only DOTS client communicates with IPv4-only alternate DOTS server.

5.6. Heartbeat Mechanism

While the communication between the DOTS agents is quiescent, the DOTS client will probe the DOTS server to ensure it has maintained cryptographic state and vice versa. Such probes can also keep alive firewall or NAT bindings. This probing reduces the frequency of needing a new handshake when a DOTS signal needs to be conveyed to the DOTS server. In DOTS over UDP, heartbeat messages can be exchanged between the DOTS agents using the "COAP ping" mechanism (Section 4.2 in [RFC7252]). The DOTS agent sends an Empty Confirmable message and the peer DOTS agent will respond by sending an Reset message. In DOTS over TCP, heartbeat messages can be exchanged between the DOTS agents using the Ping and Pong messages (Section 4.4 in [I-D.ietf-core-coap-tcp-tls]). The DOTS agent sends an Ping message and the peer DOTS agent will respond by sending an single Pong message.



6. Mapping parameters to CBOR

All parameters in DOTS signal channel are mapped to CBOR types as follows and are given an integer key value to save space.

/--------------------+------------------------+--------------------------\| Parameter name | CBOR key | CBOR major type of value ||--------------------+------------------------+--------------------------|| mitigation-scope | 1 | 5 (map) || scope | 2 | 5 (map) || mitigation-id | 3 | 0 (unsigned) || target-ip | 4 | 4 (array) || target-port-range | 5 | 4 || lower-port | 6 | 0 || upper-port | 7 | 0 || target-protocol | 8 | 4 || fqdn | 9 | 4 || uri | 10 | 4 || alias | 11 | 4 || lifetime | 12 | 0 || attack-status | 13 | 0 || signal-config | 14 | 5 || heartbeat-timeout | 15 | 0 || max-retransmit | 16 | 0 || ack-timeout | 17 | 0 || ack-random-factor | 18 | 7 || MinValue | 19 | 0 || MaxValue | 20 | 0 || status | 21 | 0 || bytes-dropped | 22 | 0 || bps-dropped | 23 | 0 || pkts-dropped | 24 | 0 || pps-dropped | 25 | 0 || session-id | 26 | 0 |\--------------------+------------------------+--------------------------/

Figure 21: CBOR mappings used in DOTS signal channel message

7. (D)TLS Protocol Profile and Performance considerations

This section defines the (D)TLS protocol profile of DOTS signal channel over (D)TLS and DOTS data channel over TLS.

There are known attacks on (D)TLS, such as machine-in-the-middle and protocol downgrade. These are general attacks on (D)TLS and not specific to DOTS over (D)TLS; please refer to the (D)TLS RFCs for discussion of these security issues. DOTS agents MUST adhere to the (D)TLS implementation recommendations and security considerations of



[RFC7525] except with respect to (D)TLS version. Since encryption of DOTS using (D)TLS is virtually a green-field deployment DOTS agents MUST implement only (D)TLS 1.2 or later.

Implementations compliant with this profile MUST implement all of the following items:

o DOTS agents MUST support DTLS record replay detection (Section 3.3 in [RFC6347]) to protect against replay attacks.

o DOTS client can use (D)TLS session resumption without server-side state [RFC5077] to resume session and convey the DOTS signal.

o Raw public keys [RFC7250] which reduce the size of the ServerHello, and can be used by servers that cannot obtain certificates (e.g., DOTS gateways on private networks).

Implementations compliant with this profile SHOULD implement all of the following items to reduce the delay required to deliver a DOTS signal:

o TLS False Start [RFC7918] which reduces round-trips by allowing the TLS second flight of messages (ChangeCipherSpec) to also contain the DOTS signal.

o Cached Information Extension [RFC7924] which avoids transmitting the server’s certificate and certificate chain if the client has cached that information from a previous TLS handshake.

o TCP Fast Open [RFC7413] can reduce the number of round-trips to convey DOTS signal.

7.1. MTU and Fragmentation Issues

To avoid DOTS signal message fragmentation and the consequently decreased probability of message delivery, DOTS agents MUST ensure that the DTLS record MUST fit within a single datagram. If the Path MTU is not known to the DOTS server, an IP MTU of 1280 bytes SHOULD be assumed. The length of the URL MUST NOT exceed 256 bytes. If UDP is used to convey the DOTS signal messages then the DOTS client must consider the amount of record expansion expected by the DTLS processing when calculating the size of CoAP message that fits within the path MTU. Path MTU MUST be greater than or equal to [CoAP message size + DTLS overhead of 13 octets + authentication overhead of the negotiated DTLS cipher suite + block padding (Section 4.1.1.1 of [RFC6347]]. If the request size exceeds the Path MTU then the DOTS client MUST split the DOTS signal into separate messages, for example the list of addresses in the ’target-ip’ parameter could be



split into multiple lists and each list conveyed in a new POST request.

Implementation Note: DOTS choice of message size parameters works well with IPv6 and with most of today’s IPv4 paths. However, with IPv4, it is harder to absolutely ensure that there is no IP fragmentation. If IPv4 support on unusual networks is a consideration and path MTU is unknown, implementations may want to limit themselves to more conservative IPv4 datagram sizes such as 576 bytes, as per [RFC0791] IP packets up to 576 bytes should never need to be fragmented, thus sending a maximum of 500 bytes of DOTS signal over a UDP datagram will generally avoid IP fragmentation.

8. (D)TLS 1.3 considerations

TLS 1.3 [I-D.ietf-tls-tls13] provides critical latency improvements for connection establishment over TLS 1.2. The DTLS 1.3 protocol [I-D.rescorla-tls-dtls13] is based on the TLS 1.3 protocol and provides equivalent security guarantees. (D)TLS 1.3 provides two basic handshake modes of interest to DOTS signal channel:

o Absent packet loss, a full handshake in which the DOTS client is able to send the DOTS signal message after one round trip and the DOTS server immediately after receiving the first DOTS signal message from the client.

o 0-RTT mode in which the DOTS client can authenticate itself and send DOTS signal message on its first flight, thus reducing handshake latency. 0-RTT only works if the DOTS client has previously communicated with that DOTS server, which is very likely with the DOTS signal channel. The DOTS client SHOULD establish a (D)TLS session with the DOTS server during peacetime and share a PSK. During DDOS attack, the DOTS client can use the (D)TLS session to convey the DOTS signal message and if there is no response from the server after multiple re-tries then the DOTS client can resume the (D)TLS session in 0-RTT mode using PSK. A simplified TLS 1.3 handshake with 0-RTT DOTS signal message exchange is shown in Figure 22.



DOTS Client DOTS Server

ClientHello (Finished) (0-RTT DOTS signal message) (end_of_early_data) --------> ServerHello {EncryptedExtensions} {ServerConfiguration} {Certificate} {CertificateVerify} {Finished} <-------- [DOTS signal message] {Finished} -------->

[DOTS signal message] <-------> [DOTS signal message]

Figure 22: TLS 1.3 handshake with 0-RTT

9. Mutual Authentication of DOTS Agents & Authorization of DOTS Clients

(D)TLS based on client certificate can be used for mutual authentication between DOTS agents. If a DOTS gateway is involved, DOTS clients and DOTS gateway MUST perform mutual authentication; only authorized DOTS clients are allowed to send DOTS signals to a DOTS gateway. DOTS gateway and DOTS server MUST perform mutual authentication; DOTS server only allows DOTS signals from authorized DOTS gateway, creating a two-link chain of transitive authentication between the DOTS client and the DOTS server.



+-------------------------------------------------+ | example.com domain +---------+ | | | AAA | | | +---------------+ | Server | | | | Application | +------+--+ | | | server + ^ | | (DOTS client) |<-----------------+ | | | +---------------+ + | | example.net domain | V V | | +-------------+ | +---------------+ | +--------------+ | | | | | | | Guest +<-----x----->+ +<---------------->+ DOTS | | | (DOTS client)| | DOTS | | | Server | | +--------------+ | Gateway | | | | | +----+--------+ | +---------------+ | ^ | | | | | +----------------+ | | | | DDOS detector | | | | | (DOTS client) +<--------------+ | | +----------------+ | | | +-------------------------------------------------+

Figure 23: Example of Authentication and Authorization of DOTS Agents

In the example depicted in Figure 23, the DOTS gateway and DOTS clients within the ’example.com’ domain mutually authenticate with each other. After the DOTS gateway validates the identity of a DOTS client, it communicates with the AAA server in the ’example.com’ domain to determine if the DOTS client is authorized to request DDOS mitigation. If the DOTS client is not authorized, a 4.01 (Unauthorized) is returned in the response to the DOTS client. In this example, the DOTS gateway only allows the application server and DDOS detector to request DDOS mitigation, but does not permit the user of type ’guest’ to request DDOS mitigation.

Also, DOTS gateway and DOTS server MUST perform mutual authentication using certificates. A DOTS server will only allow a DOTS gateway with a certificate for a particular domain to request mitigation for that domain. In reference to Figure 23, the DOTS server only allows the DOTS gateway to request mitigation for ’example.com’ domain and not for other domains.




This specification registers new parameters for DOTS signal channel and establishes registries for mappings to CBOR.

10.1. DOTS signal channel CBOR Mappings Registry

A new registry will be requested from IANA, entitled "DOTS signal channel CBOR Mappings Registry". The registry is to be created as Expert Review Required.

10.1.1. Registration Template

Parameter name: Parameter names (e.g., "target_ip") in the DOTS signal channel.

CBOR Key Value: Key value for the parameter. The key value MUST be an integer in the range of 1 to 65536. The key values in the range of 32768 to 65536 are assigned for Vendor-Specific parameters.

CBOR Major Type: CBOR Major type and optional tag for the claim.

Change Controller: For Standards Track RFCs, list the "IESG". For others, give the name of the responsible party. Other details (e.g., postal address, email address, home page URI) may also be included.


10.1.2. Initial Registry Contents

o Parameter Name: "mitigation-scope" o CBOR Key Value: 1 o CBOR Major Type: 5 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: "scope" o CBOR Key Value: 2 o CBOR Major Type: 5 o Change Controller: IESG o Specification Document(s): this document



o Parameter Name: "mitigation-id" o CBOR Key Value: 3 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name:target-ip o CBOR Key Value: 4 o CBOR Major Type: 4 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: target-port-range o CBOR Key Value: 5 o CBOR Major Type: 4 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: "lower-port" o CBOR Key Value: 6 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: "upper-port" o CBOR Key Value: 7 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: target-protocol o CBOR Key Value: 8 o CBOR Major Type: 4 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: "FQDN" o CBOR Key Value: 9 o CBOR Major Type: 4 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: "URI" o CBOR Key Value: 10 o CBOR Major Type: 4 o Change Controller: IESG o Specification Document(s): this document



o Parameter Name: alias o CBOR Key Value: 11 o CBOR Major Type: 4 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: "lifetime" o CBOR Key Value: 12 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: attack-status o CBOR Key Value: 13 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: signal-config o CBOR Key Value: 14 o CBOR Major Type: 5 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: heartbeat-timeout o CBOR Key Value: 15 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: max-retransmit o CBOR Key Value: 16 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: ack-timeout o CBOR Key Value: 17 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: ack-random-factor o CBOR Key Value: 18 o CBOR Major Type: 7 o Change Controller: IESG o Specification Document(s): this document



o Parameter Name: MinValue o CBOR Key Value: 19 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: MaxValue o CBOR Key Value: 20 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: status o CBOR Key Value: 21 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: bytes-dropped o CBOR Key Value: 22 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: bps-dropped o CBOR Key Value: 23 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: pkts-dropped o CBOR Key Value: 24 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: pps-dropped o CBOR Key Value: 25 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document

o Parameter Name: session-id o CBOR Key Value: 26 o CBOR Major Type: 0 o Change Controller: IESG o Specification Document(s): this document



11. Implementation Status

[Note to RFC Editor: Please remove this section and reference to [RFC7942] prior to publication.]

This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC7942]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist.

According to [RFC7942], "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit".

11.1. nttdots

Organization: NTT Communication is developing a DOTS client and DOTS server software based on DOTS signal channel specified in this draft. It will be open-sourced. Description: Early implementation of DOTS protocol. It is aimed to implement a full DOTS protocol spec in accordance with maturing of DOTS protocol itself. Implementation: To be open-sourced. Level of maturity: It is a early implementation of DOTS protocol. Messaging between DOTS clients and DOTS servers has been tested. Level of maturity will increase in accordance with maturing of DOTS protocol itself. Coverage: Capability of DOTS client: sending DOTS messages to the DOTS server in CoAP over DTLS as dots-signal. Capability of DOTS server: receiving dots-signal, validating received dots-signal, starting mitigation by handing over the dots-signal to DDOS mitigator. Licensing: It will be open-sourced with BSD 3-clause license. Implementation experience: It is implemented in Go-lang. Core specification of signaling is mature to be implemented, however, finding good libraries(like DTLS, CoAP) is rather difficult. Contact: Kaname Nishizuka <[email protected]>




Authenticated encryption MUST be used for data confidentiality and message integrity. (D)TLS based on client certificate MUST be used for mutual authentication. The interaction between the DOTS agents requires Datagram Transport Layer Security (DTLS) and Transport Layer Security (TLS) with a cipher suite offering confidentiality protection and the guidance given in [RFC7525] MUST be followed to avoid attacks on (D)TLS.

A single DOTS signal channel between DOTS agents can be used to exchange multiple DOTS signal messages. To reduce DOTS client and DOTS server workload, DOTS client SHOULD re-use the (D)TLS session.

If TCP is used between DOTS agents, an attacker may be able to inject RST packets, bogus application segments, etc., regardless of whether TLS authentication is used. Because the application data is TLS protected, this will not result in the application receiving bogus data, but it will constitute a DoS on the connection. This attack can be countered by using TCP-AO [RFC5925]. If TCP-AO is used, then any bogus packets injected by an attacker will be rejected by the TCP-AO integrity check and therefore will never reach the TLS layer.

Special care should be taken in order to ensure that the activation of the proposed mechanism won’t have an impact on the stability of the network (including connectivity and services delivered over that network).

Involved functional elements in the cooperation system must establish exchange instructions and notification over a secure and authenticated channel. Adequate filters can be enforced to avoid that nodes outside a trusted domain can inject request such as deleting filtering rules. Nevertheless, attacks can be initiated from within the trusted domain if an entity has been corrupted. Adequate means to monitor trusted nodes should also be enabled.

13. Contributors


Mike Geller Cisco Systems, Inc. 3250 Florida 33309 USA Email: [email protected]

Robert Moskowitz HTT Consulting Oak Park, MI 42837 United States Email: [email protected]

Dan Wing Email: [email protected]




Thanks to Christian Jacquenet, Roland Dobbins, Andrew Mortensen, Roman D. Danyliw, Michael Richardson, Ehud Doron, Kaname Nishizuka, Dave Dolson, Liang Xia and Gilbert Clark for the discussion and comments.

15. References


[I-D.ietf-core-coap-tcp-tls] Bormann, C., Lemay, S., Tschofenig, H., Hartke, K., Silverajan, B., and B. Raymor, "CoAP (Constrained Application Protocol) over TCP, TLS, and WebSockets", draft-ietf-core-coap-tcp-tls-09 (work in progress), May 2017.



[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP Authentication Option", RFC 5925, DOI 10.17487/RFC5925, June 2010, <http://www.rfc-editor.org/info/rfc5925>.


[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J., Weiler, S., and T. Kivinen, "Using Raw Public Keys in Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250, June 2014, <http://www.rfc-editor.org/info/rfc7250>.

[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, <http://www.rfc-editor.org/info/rfc7252>.



[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, "Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 2015, <http://www.rfc-editor.org/info/rfc7525>.

[RFC7641] Hartke, K., "Observing Resources in the Constrained Application Protocol (CoAP)", RFC 7641, DOI 10.17487/RFC7641, September 2015, <http://www.rfc-editor.org/info/rfc7641>.


[I-D.ietf-core-comi] Stok, P., Bierman, A., Veillette, M., and A. Pelov, "CoAP Management Interface", draft-ietf-core-comi-00 (work in progress), January 2017.

[I-D.ietf-core-yang-cbor] Veillette, M., Pelov, A., Somaraju, A., Turner, R., and A. Minaburo, "CBOR Encoding of Data Modeled with YANG", draft-ietf-core-yang-cbor-04 (work in progress), February 2017.


[I-D.ietf-dots-data-channel] Reddy, T., Boucadair, M., Nishizuka, K., Xia, L., Patil, P., Mortensen, A., and N. Teague, "Distributed Denial-of- Service Open Threat Signaling (DOTS) Data Channel", draft- ietf-dots-data-channel-01 (work in progress), June 2017.





[I-D.ietf-tls-tls13] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", draft-ietf-tls-tls13-20 (work in progress), April 2017.

[I-D.rescorla-tls-dtls13] Rescorla, E., Tschofenig, H., and N. Modadugu, "The Datagram Transport Layer Security (DTLS) Protocol Version 1.3", draft-rescorla-tls-dtls13-01 (work in progress), March 2017.

[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 10.17487/RFC0791, September 1981, <http://www.rfc-editor.org/info/rfc791>.

[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 2006, <http://www.rfc-editor.org/info/rfc4632>.


[RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common Mitigations", RFC 4987, DOI 10.17487/RFC4987, August 2007, <http://www.rfc-editor.org/info/rfc4987>.

[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, "Transport Layer Security (TLS) Session Resumption without Server-Side State", RFC 5077, DOI 10.17487/RFC5077, January 2008, <http://www.rfc-editor.org/info/rfc5077>.

[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, <http://www.rfc-editor.org/info/rfc6020>.

[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, April 2012, <http://www.rfc-editor.org/info/rfc6555>.

[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown, "Default Address Selection for Internet Protocol Version 6 (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012, <http://www.rfc-editor.org/info/rfc6724>.



[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October 2013, <http://www.rfc-editor.org/info/rfc7049>.

[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, <http://www.rfc-editor.org/info/rfc7413>.

[RFC7589] Badra, M., Luchuk, A., and J. Schoenwaelder, "Using the NETCONF Protocol over Transport Layer Security (TLS) with Mutual X.509 Authentication", RFC 7589, DOI 10.17487/RFC7589, June 2015, <http://www.rfc-editor.org/info/rfc7589>.

[RFC7918] Langley, A., Modadugu, N., and B. Moeller, "Transport Layer Security (TLS) False Start", RFC 7918, DOI 10.17487/RFC7918, August 2016, <http://www.rfc-editor.org/info/rfc7918>.

[RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security (TLS) Cached Information Extension", RFC 7924, DOI 10.17487/RFC7924, July 2016, <http://www.rfc-editor.org/info/rfc7924>.

[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", BCP 205, RFC 7942, DOI 10.17487/RFC7942, July 2016, <http://www.rfc-editor.org/info/rfc7942>.

[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, March 2017, <http://www.rfc-editor.org/info/rfc8085>.












Nik Teague Verisign, Inc. United States



DOTS T. Reddy, Ed.Internet-Draft McAfeeIntended status: Standards Track M. Boucadair, Ed.Expires: July 9, 2020 Orange P. Patil Cisco A. Mortensen Arbor Networks, Inc. N. Teague Iron Mountain Data Centers January 6, 2020

Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification draft-ietf-dots-signal-channel-41

Abstract

This document specifies the DOTS signal channel, a protocol for signaling the need for protection against Distributed Denial-of- Service (DDoS) attacks to a server capable of enabling network traffic mitigation on behalf of the requesting client.

A companion document defines the DOTS data channel, a separate reliable communication layer for DOTS management and configuration purposes.

Editorial Note (To be removed by RFC Editor)

Please update these statements within the document with the RFC number to be assigned to this document:

o "This version of this YANG module is part of RFC XXXX;"

o "RFC XXXX: Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification";

o "| [RFCXXXX] |"

o reference: RFC XXXX

Please update this statement with the RFC number to be assigned to the following documents:

o "RFC YYYY: Distributed Denial-of-Service Open Threat Signaling (DOTS) Data Channel Specification (used to be I-D.ietf-dots-data- channel)

Reddy, et al. Expires July 9, 2020 [Page 1]

Internet-Draft DOTS Signal Channel Protocol January 2020

Please update TBD/TBD1/TBD2 statements with the assignments made by IANA to DOTS Signal Channel Protocol.

Also, please update the "revision" date of the YANG modules.

Status of This Memo




This Internet-Draft will expire on July 9, 2020.

Copyright Notice



Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Design Overview . . . . . . . . . . . . . . . . . . . . . . . 6 4. DOTS Signal Channel: Messages & Behaviors . . . . . . . . . . 10 4.1. DOTS Server(s) Discovery . . . . . . . . . . . . . . . . 10 4.2. CoAP URIs . . . . . . . . . . . . . . . . . . . . . . . . 10 4.3. Happy Eyeballs for DOTS Signal Channel . . . . . . . . . 10 4.4. DOTS Mitigation Methods . . . . . . . . . . . . . . . . . 12 4.4.1. Request Mitigation . . . . . . . . . . . . . . . . . 13



4.4.2. Retrieve Information Related to a Mitigation . . . . 29 4.4.2.1. DOTS Servers Sending Mitigation Status . . . . . 34 4.4.2.2. DOTS Clients Polling for Mitigation Status . . . 37 4.4.3. Efficacy Update from DOTS Clients . . . . . . . . . . 38 4.4.4. Withdraw a Mitigation . . . . . . . . . . . . . . . . 40 4.5. DOTS Signal Channel Session Configuration . . . . . . . . 41 4.5.1. Discover Configuration Parameters . . . . . . . . . . 43 4.5.2. Convey DOTS Signal Channel Session Configuration . . 48 4.5.3. Configuration Freshness and Notifications . . . . . . 53 4.5.4. Delete DOTS Signal Channel Session Configuration . . 54 4.6. Redirected Signaling . . . . . . . . . . . . . . . . . . 55 4.7. Heartbeat Mechanism . . . . . . . . . . . . . . . . . . . 57 5. DOTS Signal Channel YANG Modules . . . . . . . . . . . . . . 60 5.1. Tree Structure . . . . . . . . . . . . . . . . . . . . . 60 5.2. IANA DOTS Signal Channel YANG Module . . . . . . . . . . 62 5.3. IETF DOTS Signal Channel YANG Module . . . . . . . . . . 66 6. YANG/JSON Mapping Parameters to CBOR . . . . . . . . . . . . 77 7. (D)TLS Protocol Profile and Performance Considerations . . . 79 7.1. (D)TLS Protocol Profile . . . . . . . . . . . . . . . . . 79 7.2. (D)TLS 1.3 Considerations . . . . . . . . . . . . . . . . 81 7.3. DTLS MTU and Fragmentation . . . . . . . . . . . . . . . 83 8. Mutual Authentication of DOTS Agents & Authorization of DOTS Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 86 9.1. DOTS Signal Channel UDP and TCP Port Number . . . . . . . 86 9.2. Well-Known ’dots’ URI . . . . . . . . . . . . . . . . . . 86 9.3. Media Type Registration . . . . . . . . . . . . . . . . . 86 9.4. CoAP Content-Formats Registration . . . . . . . . . . . . 87 9.5. CBOR Tag Registration . . . . . . . . . . . . . . . . . . 87 9.6. DOTS Signal Channel Protocol Registry . . . . . . . . . . 88 9.6.1. DOTS Signal Channel CBOR Key Values Sub-Registry . . 88 9.6.1.1. Registration Template . . . . . . . . . . . . . . 88 9.6.1.2. Initial Sub-Registry Content . . . . . . . . . . 89 9.6.2. Status Codes Sub-Registry . . . . . . . . . . . . . . 91 9.6.3. Conflict Status Codes Sub-Registry . . . . . . . . . 92 9.6.4. Conflict Cause Codes Sub-Registry . . . . . . . . . . 94 9.6.5. Attack Status Codes Sub-Registry . . . . . . . . . . 94 9.7. DOTS Signal Channel YANG Modules . . . . . . . . . . . . 95 10. Security Considerations . . . . . . . . . . . . . . . . . . . 96 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 98 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 99 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 99 13.1. Normative References . . . . . . . . . . . . . . . . . . 99 13.2. Informative References . . . . . . . . . . . . . . . . . 102 Appendix A. CUID Generation . . . . . . . . . . . . . . . . . . 107 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 107



1. Introduction

A distributed denial-of-service (DDoS) attack is a distributed attempt to make machines or network resources unavailable to their intended users. In most cases, sufficient scale for an effective attack can be achieved by compromising enough end-hosts and using those infected hosts to perpetrate and amplify the attack. The victim in this attack can be an application server, a host, a router, a firewall, or an entire network.

Network applications have finite resources like CPU cycles, the number of processes or threads they can create and use, the maximum number of simultaneous connections they can handle, the limited resources of the control plane, etc. When processing network traffic, such applications are supposed to use these resources to provide the intended functionality in the most efficient manner. However, a DDoS attacker may be able to prevent an application from performing its intended task by making the application exhaust its finite resources.

A TCP DDoS SYN-flood [RFC4987], for example, is a memory-exhausting attack while an ACK-flood is a CPU-exhausting attack. Attacks on the link are carried out by sending enough traffic so that the link becomes congested, thereby likely causing packet loss for legitimate traffic. Stateful firewalls can also be attacked by sending traffic that causes the firewall to maintain an excessive number of states that may jeopardize the firewall’s operation overall, besides likely performance impacts. The firewall then runs out of memory, and can no longer instantiate the states required to process legitimate flows. Other possible DDoS attacks are discussed in [RFC4732].

In many cases, it may not be possible for network administrators to determine the cause(s) of an attack. They may instead just realize that certain resources seem to be under attack. This document defines a lightweight protocol that allows a DOTS client to request mitigation from one or more DOTS servers for protection against detected, suspected, or anticipated attacks. This protocol enables cooperation between DOTS agents to permit a highly-automated network defense that is robust, reliable, and secure. Note that "secure" means the support of the features defined in Section 2.4 of [RFC8612].

An example of a network diagram that illustrates a deployment of DOTS agents is shown in Figure 1. In this example, a DOTS server is operating on the access network. A DOTS client is located on the LAN (Local Area Network), while a DOTS gateway is embedded in the CPE (Customer Premises Equipment).



Network Resource CPE router Access network __________ +-----------+ +--------------+ +-------------+ / \ | |___| |____| |___ | Internet | |DOTS client| | DOTS gateway | | DOTS server | | | | | | | | | | | +-----------+ +--------------+ +-------------+ \__________/


DOTS servers can also be reachable over the Internet, as depicted in Figure 2.

Network DDoS mitigation Resource CPE router __________ service +-----------+ +-------------+ / \ +-------------+ | |___| |____| |___ | | |DOTS client| |DOTS gateway | | Internet | | DOTS server | | | | | | | | | +-----------+ +-------------+ \__________/ +-------------+


In typical deployments, the DOTS client belongs to a different administrative domain than the DOTS server. For example, the DOTS client is embedded in a firewall protecting services owned and operated by a customer, while the DOTS server is owned and operated by a different administrative entity (service provider, typically) providing DDoS mitigation services. The latter might or might not provide connectivity services to the network hosting the DOTS client.

The DOTS server may (not) be co-located with the DOTS mitigator. In typical deployments, the DOTS server belongs to the same administrative domain as the mitigator. The DOTS client can communicate directly with a DOTS server or indirectly via a DOTS gateway.

The document adheres to the DOTS architecture [I-D.ietf-dots-architecture]. The requirements for DOTS signal channel protocol are documented in [RFC8612]. This document satisfies all the use cases discussed in [I-D.ietf-dots-use-cases].

This document focuses on the DOTS signal channel. This is a companion document of the DOTS data channel specification [I-D.ietf-dots-data-channel] that defines a configuration and a bulk data exchange mechanism supporting the DOTS signal channel.



2. Terminology


(D)TLS is used for statements that apply to both Transport Layer Security [RFC5246][RFC8446] and Datagram Transport Layer Security [RFC6347]. Specific terms are used for any statement that applies to either protocol alone.

The reader should be familiar with the terms defined in [RFC8612].

The meaning of the symbols in YANG tree diagrams is defined in [RFC8340].

3. Design Overview

The DOTS signal channel is built on top of the Constrained Application Protocol (CoAP) [RFC7252], a lightweight protocol originally designed for constrained devices and networks. The many features of CoAP (expectation of packet loss, support for asynchronous Non-confirmable messaging, congestion control, small message overhead limiting the need for fragmentation, use of minimal resources, and support for (D)TLS) makes it a good candidate to build the DOTS signaling mechanism from.

DOTS clients and servers behave as CoAP endpoints. By default, a DOTS client (or server) behaves as a CoAP client (or server). Nevertheless, a DOTS client (or server) behaves as a CoAP server (or client) for specific operations such as DOTS heartbeat operations (Section 4.7).

The DOTS signal channel is layered on existing standards (Figure 3).



+---------------------+ | DOTS Signal Channel | +---------------------+ | CoAP | +----------+----------+ | TLS | DTLS | +----------+----------+ | TCP | UDP | +----------+----------+ | IP | +---------------------+

Figure 3: Abstract Layering of DOTS Signal Channel over CoAP over (D)TLS

In some cases, a DOTS client and server may have mutual agreement to use a specific port number, such as by explicit configuration or dynamic discovery [I-D.ietf-dots-server-discovery]. Absent such mutual agreement, the DOTS signal channel MUST run over port number TBD as defined in Section 9.1, for both UDP and TCP. In order to use a distinct port number (as opposed to TBD), DOTS clients and servers SHOULD support a configurable parameter to supply the port number to use.

Note: The rationale for not using the default port number 5684 ((D)TLS CoAP) is to avoid the discovery of services and resources discussed in [RFC7252] and allow for differentiated behaviors in environments where both a DOTS gateway and an IoT gateway (e.g., Figure 3 of [RFC7452]) are co-located.

Particularly, the use of a default port number is meant to simplify DOTS deployment in scenarios where no explicit IP address configuration is required. For example, the use of the default router as DOTS server aims to ease DOTS deployment within LANs (in which, CPEs embed a DOTS gateway as illustrated in Figures 1 and 2) without requiring a sophisticated discovery method and configuration tasks within the LAN. It is also possible to use anycast addresses for DOTS servers to simplify DOTS client configuration, including service discovery. In such anycast-based scenario, a DOTS client initiating a DOTS session to the DOTS server anycast address may, for example, be (1) redirected to the DOTS server unicast address to be used by the DOTS client following the procedure discussed in Section 4.6 or (2) relayed to a unicast DOTS server.

The signal channel uses the "coaps" URI scheme defined in Section 6 of [RFC7252] and the "coaps+tcp" URI scheme defined in Section 8.2 of [RFC8323] to identify DOTS server resources accessible using CoAP



over UDP secured with DTLS and CoAP over TCP secured with TLS, respectively.

The DOTS signal channel can be established between two DOTS agents prior or during an attack. The DOTS signal channel is initiated by the DOTS client. The DOTS client can then negotiate, configure, and retrieve the DOTS signal channel session behavior with its DOTS peer (Section 4.5). Once the signal channel is established, the DOTS agents may periodically send heartbeats to keep the channel active (Section 4.7). At any time, the DOTS client may send a mitigation request message (Section 4.4) to a DOTS server over the active signal channel. While mitigation is active (because of the higher likelihood of packet loss during a DDoS attack), the DOTS server periodically sends status messages to the client, including basic mitigation feedback details. Mitigation remains active until the DOTS client explicitly terminates mitigation, or the mitigation lifetime expires. Also, the DOTS server may rely on the signal channel session loss to trigger mitigation for pre-configured mitigation requests (if any).

DOTS signaling can happen with DTLS over UDP and TLS over TCP. Likewise, DOTS requests may be sent using IPv4 or IPv6 transfer capabilities. A Happy Eyeballs procedure for DOTS signal channel is specified in Section 4.3.

A DOTS client is entitled to access only to resources it creates. In particular, a DOTS client can not retrieve data related to mitigation requests created by other DOTS clients of the same DOTS client domain.

Messages exchanged between DOTS agents are serialized using Concise Binary Object Representation (CBOR) [RFC7049], a binary encoding scheme designed for small code and message size. CBOR-encoded payloads are used to carry signal channel-specific payload messages which convey request parameters and response information such as errors. In order to allow reusing data models across protocols, [RFC7951] specifies the JavaScript Object Notation (JSON) encoding of YANG-modeled data. A similar effort for CBOR is defined in [I-D.ietf-core-yang-cbor].

DOTS agents determine that a CBOR data structure is a DOTS signal channel object from the application context, such as from the port number assigned to the DOTS signal channel. The other method DOTS agents use to indicate that a CBOR data structure is a DOTS signal channel object is the use of the "application/dots+cbor" content type (Section 9.3).



This document specifies a YANG module for representing DOTS mitigation scopes, DOTS signal channel session configuration data, and DOTS redirected signaling (Section 5). All parameters in the payload of the DOTS signal channel are mapped to CBOR types as specified in Table 4 (Section 6).

In order to prevent fragmentation, DOTS agents must follow the recommendations documented in Section 4.6 of [RFC7252]. Refer to Section 7.3 for more details.

DOTS agents MUST support GET, PUT, and DELETE CoAP methods. The payload included in CoAP responses with 2.xx Response Codes MUST be of content type "application/dots+cbor". CoAP responses with 4.xx and 5.xx error Response Codes MUST include a diagnostic payload (Section 5.5.2 of [RFC7252]). The Diagnostic Payload may contain additional information to aid troubleshooting.

In deployments where multiple DOTS clients are enabled in a network (owned and operated by the same entity), the DOTS server may detect conflicting mitigation requests from these clients. This document does not aim to specify a comprehensive list of conditions under which a DOTS server will characterize two mitigation requests from distinct DOTS clients as conflicting, nor recommend a DOTS server behavior for processing conflicting mitigation requests. Those considerations are implementation- and deployment-specific. Nevertheless, the document specifies the mechanisms to notify DOTS clients when conflicts occur, including the conflict cause (Section 4.4).

In deployments where one or more translators (e.g., Traditional NAT [RFC3022], CGN [RFC6888], NAT64 [RFC6146], NPTv6 [RFC6296]) are enabled between the client’s network and the DOTS server, DOTS signal channel messages forwarded to a DOTS server MUST NOT include internal IP addresses/prefixes and/or port numbers; external addresses/ prefixes and/or port numbers as assigned by the translator MUST be used instead. This document does not make any recommendation about possible translator discovery mechanisms. The following are some (non-exhaustive) deployment examples that may be considered:

o Port Control Protocol (PCP) [RFC6887] or Session Traversal Utilities for NAT (STUN) [RFC5389] may be used to retrieve the external addresses/prefixes and/or port numbers. Information retrieved by means of PCP or STUN will be used to feed the DOTS signal channel messages that will be sent to a DOTS server.

o A DOTS gateway may be co-located with the translator. The DOTS gateway will need to update the DOTS messages, based upon the local translator’s binding table.



4. DOTS Signal Channel: Messages & Behaviors

4.1. DOTS Server(s) Discovery

This document assumes that DOTS clients are provisioned with the reachability information of their DOTS server(s) using any of a variety of means (e.g., local configuration, or dynamic means such as DHCP [I-D.ietf-dots-server-discovery]). The description of such means is out of scope of this document.

Likewise, it is out of scope of this document to specify the behavior to be followed by a DOTS client to send DOTS requests when multiple DOTS servers are provisioned (e.g., contact all DOTS servers, select one DOTS server among the list). Such behavior is specified in other documents (e.g., [I-D.ietf-dots-multihoming]).

4.2. CoAP URIs

The DOTS server MUST support the use of the path-prefix of "/.well- known/" as defined in [RFC8615] and the registered name of "dots". Each DOTS operation is indicated by a path-suffix that indicates the intended operation. The operation path (Table 1) is appended to the path-prefix to form the URI used with a CoAP request to perform the desired DOTS operation.

+-----------------------+----------------+-------------+ | Operation | Operation Path | Details | +-----------------------+----------------+-------------+ | Mitigation | /mitigate | Section 4.4 | +-----------------------+----------------+-------------+ | Session configuration | /config | Section 4.5 | +-----------------------+----------------+-------------+ | Heartbeat | /hb | Section 4.7 | +-----------------------+----------------+-------------+

Table 1: Operations and their Corresponding URIs

4.3. Happy Eyeballs for DOTS Signal Channel

[RFC8612] mentions that DOTS agents will have to support both connectionless and connection-oriented protocols. As such, the DOTS signal channel is designed to operate with DTLS over UDP and TLS over TCP. Further, a DOTS client may acquire a list of IPv4 and IPv6 addresses (Section 4.1), each of which can be used to contact the DOTS server using UDP and TCP. If no list of IPv4 and IPv6 addresses to contact the DOTS server is configured (or discovered), the DOTS client adds the IPv4/IPv6 addresses of its default router to the candidate list to contact the DOTS server.



The following specifies the procedure to follow to select the address family and the transport protocol for sending DOTS signal channel messages.

Such procedure is needed to avoid experiencing long connection delays. For example, if an IPv4 path to reach a DOTS server is functional, but the DOTS server’s IPv6 path is non-functional, a dual-stack DOTS client may experience a significant connection delay compared to an IPv4-only DOTS client, in the same network conditions. The other problem is that if a middlebox between the DOTS client and DOTS server is configured to block UDP traffic, the DOTS client will fail to establish a DTLS association with the DOTS server and, as a consequence, will have to fall back to TLS over TCP, thereby incurring significant connection delays.

To overcome these connection setup problems, the DOTS client attempts to connect to its DOTS server(s) using both IPv6 and IPv4, and tries both DTLS over UDP and TLS over TCP following a DOTS Happy Eyeballs approach. To some extent, this approach is similar to the Happy Eyeballs mechanism defined in [RFC8305]. The connection attempts are performed by the DOTS client when it initializes, or in general when it has to select an address family and transport to contact its DOTS server. The results of the Happy Eyeballs procedure are used by the DOTS client for sending its subsequent messages to the DOTS server. The difference in behavior with respect to the Happy Eyeballs mechanism [RFC8305] are listed below:

o The order of preference of the DOTS signal channel address family and transport protocol (most preferred first) is: UDP over IPv6, UDP over IPv4, TCP over IPv6, and finally TCP over IPv4. This order adheres to the address preference order specified in [RFC6724] and the DOTS signal channel preference which privileges the use of UDP over TCP (to avoid TCP’s head of line blocking).

o The DOTS client after successfully establishing a connection MUST cache information regarding the outcome of each connection attempt for a specific time period, and it uses that information to avoid thrashing the network with subsequent attempts. The cached information is flushed when its age exceeds a specific time period on the order of few minutes (e.g., 10 min). Typically, if the DOTS client has to re-establish the connection with the same DOTS server within few seconds after the Happy Eyeballs mechanism is completed, caching avoids trashing the network especially in the presence of DDoS attack traffic.

o If DOTS signal channel session is established with TLS (but DTLS failed), the DOTS client periodically repeats the mechanism to discover whether DOTS signal channel messages with DTLS over UDP



becomes available from the DOTS server, so the DOTS client can migrate the DOTS signal channel from TCP to UDP. Such probing SHOULD NOT be done more frequently than every 24 hours and MUST NOT be done more frequently than every 5 minutes.

When connection attempts are made during an attack, the DOTS client SHOULD use a "Connection Attempt Delay" [RFC8305] set to 100 ms.

In reference to Figure 4, the DOTS client proceeds with the connection attempts following the rules in [RFC8305]. In this example, it is assumed that the IPv6 path is broken and UDP traffic is dropped by a middlebox but has little impact to the DOTS client because there is no long delay before using IPv4 and TCP.

+-----------+ +-----------+ |DOTS client| |DOTS server| +-----------+ +-----------+ | | T0 |--DTLS ClientHello, IPv6 ---->X | T1 |--DTLS ClientHello, IPv4 ---->X | T2 |--TCP SYN, IPv6-------------->X | T3 |--TCP SYN, IPv4--------------------------------------->| |<-TCP SYNACK-------------------------------------------| |--TCP ACK--------------------------------------------->| |<------------Establish TLS Session-------------------->| |----------------DOTS signal--------------------------->| | |

Note: * Retransmission messages are not shown. * T1-T0=T2-T1=T3-T2= Connection Attempt Delay.

Figure 4: DOTS Happy Eyeballs (Sample Flow)

A single DOTS signal channel between DOTS agents can be used to exchange multiple DOTS signal messages. To reduce DOTS client and DOTS server workload, DOTS clients SHOULD re-use the (D)TLS session.

4.4. DOTS Mitigation Methods

The following methods are used by a DOTS client to request, withdraw, or retrieve the status of mitigation requests:

PUT: DOTS clients use the PUT method to request mitigation from a DOTS server (Section 4.4.1). During active mitigation, DOTS clients may use PUT requests to carry mitigation efficacy updates to the DOTS server (Section 4.4.3).



GET: DOTS clients may use the GET method to subscribe to DOTS server status messages, or to retrieve the list of its mitigations maintained by a DOTS server (Section 4.4.2).

DELETE: DOTS clients use the DELETE method to withdraw a request for mitigation from a DOTS server (Section 4.4.4).

Mitigation request and response messages are marked as Non- confirmable messages (Section 2.2 of [RFC7252]).

DOTS agents MUST NOT send more than one UDP datagram per round-trip time (RTT) to the peer DOTS agent on average following the data transmission guidelines discussed in Section 3.1.3 of [RFC8085].

Requests marked by the DOTS client as Non-confirmable messages are sent at regular intervals until a response is received from the DOTS server. If the DOTS client cannot maintain an RTT estimate, it MUST NOT send more than one Non-confirmable request every 3 seconds, and SHOULD use an even less aggressive rate whenever possible (case 2 in Section 3.1.3 of [RFC8085]). Mitigation requests MUST NOT be delayed because of checks on probing rate (Section 4.7 of [RFC7252]).

JSON encoding of YANG modelled data [RFC7951] is used to illustrate the various methods defined in the following sub-sections. Also, the examples use the Labels defined in Sections 9.6.2, 9.6.3, 9.6.4, and 9.6.5.

4.4.1. Request Mitigation

When a DOTS client requires mitigation for some reason, the DOTS client uses the CoAP PUT method to send a mitigation request to its DOTS server(s) (Figures 5 and 6).

If a DOTS client is entitled to solicit the DOTS service, the DOTS server enables mitigation on behalf of the DOTS client by communicating the DOTS client’s request to a mitigator (which may be co-located with the DOTS server) and relaying the feedback of the thus-selected mitigator to the requesting DOTS client.



Header: PUT (Code=0.03) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "mitigate" Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw" Uri-Path: "mid=123" Content-Format: "application/dots+cbor"

{ ... }

Figure 5: PUT to Convey DOTS Mitigation Requests

The order of the Uri-Path options is important as it defines the CoAP resource. In particular, ’mid’ MUST follow ’cuid’.

The additional Uri-Path parameters to those defined in Section 4.2 are as follows:

cuid: Stands for Client Unique Identifier. A globally unique identifier that is meant to prevent collisions among DOTS clients, especially those from the same domain. It MUST be generated by DOTS clients.

For the reasons discussed in Appendix A, implementations SHOULD set ’cuid’ using the following procedure: first, the Distinguished Encoding Rules (DER)-encoded Abstract Syntax Notation One (ASN.1) representation of the Subject Public Key Info (SPKI) of the DOTS client X.509 certificate [RFC5280], the DOTS client raw public key [RFC7250], the "Pre-Shared Key (PSK) identity" used by the DOTS client in the TLS 1.2 ClientKeyExchange message, or the "identity" used by the DOTS client in the "pre_shared_key" TLS 1.3 extension is input to the SHA-256 [RFC6234] cryptographic hash. Then, the output of the cryptographic hash algorithm is truncated to 16 bytes; truncation is done by stripping off the final 16 bytes. The truncated output is base64url encoded (Section 5 of [RFC4648]) with the trailing "=" removed from the encoding, and the resulting value used as the ’cuid’.

The ’cuid’ is intended to be stable when communicating with a given DOTS server, i.e., the ’cuid’ used by a DOTS client SHOULD NOT change over time. Distinct ’cuid’ values MAY be used by a single DOTS client per DOTS server.

If a DOTS client has to change its ’cuid’ for some reason, it MUST NOT do so when mitigations are still active for the old



’cuid’. The ’cuid’ SHOULD be 22 characters to avoid DOTS signal message fragmentation over UDP. Furthermore, if that DOTS client created aliases and filtering entries at the DOTS server by means of the DOTS data channel, it MUST delete all the entries bound to the old ’cuid’ and re-install them using the new ’cuid’.

DOTS servers MUST return 4.09 (Conflict) error code to a DOTS peer to notify that the ’cuid’ is already in-use by another DOTS client. Upon receipt of that error code, a new ’cuid’ MUST be generated by the DOTS peer (e.g., using [RFC4122]).

Client-domain DOTS gateways MUST handle ’cuid’ collision directly and it is RECOMMENDED that ’cuid’ collision is handled directly by server-domain DOTS gateways.

DOTS gateways MAY rewrite the ’cuid’ used by peer DOTS clients. Triggers for such rewriting are out of scope.

This is a mandatory Uri-Path parameter.

mid: Identifier for the mitigation request represented with an integer. This identifier MUST be unique for each mitigation request bound to the DOTS client, i.e., the ’mid’ parameter value in the mitigation request needs to be unique (per ’cuid’ and DOTS server) relative to the ’mid’ parameter values of active mitigation requests conveyed from the DOTS client to the DOTS server.

In order to handle out-of-order delivery of mitigation requests, ’mid’ values MUST increase monotonically.

If the ’mid’ value has reached 3/4 of (2**32 - 1) (i.e., 3221225471) and no attack is detected, the DOTS client MUST reset ’mid’ to 0 to handle ’mid’ rollover. If the DOTS client maintains mitigation requests with pre-configured scopes, it MUST re-create them with the ’mid’ restarting at 0.

This identifier MUST be generated by the DOTS client.

This is a mandatory Uri-Path parameter.

’cuid’ and ’mid’ MUST NOT appear in the PUT request message body (Figure 6). The schema in Figure 6 uses the types defined in Section 6. Note that this figure (and other similar figures depicting a schema) are non-normative sketches of the structure of the message.



{ "ietf-dots-signal-channel:mitigation-scope": { "scope": [ { "target-prefix": [ "string" ], "target-port-range": [ { "lower-port": number, "upper-port": number } ], "target-protocol": [ number ], "target-fqdn": [ "string" ], "target-uri": [ "string" ], "alias-name": [ "string" ], "lifetime": number, "trigger-mitigation": true|false } ] } }

Figure 6: PUT to Convey DOTS Mitigation Requests (Message Body Schema)

The parameters in the CBOR body (Figure 6) of the PUT request are described below:

target-prefix: A list of prefixes identifying resources under attack. Prefixes are represented using Classless Inter-Domain Routing (CIDR) notation [RFC4632]. As a reminder, the prefix length must be less than or equal to 32 (or 128) for IPv4 (or IPv6).

The prefix list MUST NOT include broadcast, loopback, or multicast addresses. These addresses are considered as invalid values. In addition, the DOTS server MUST validate that target prefixes are



within the scope of the DOTS client domain. Other validation checks may be supported by DOTS servers.


target-port-range: A list of port numbers bound to resources under attack.

A port range is defined by two bounds, a lower port number (lower- port) and an upper port number (upper-port). When only ’lower- port’ is present, it represents a single port number.

For TCP, UDP, Stream Control Transmission Protocol (SCTP) [RFC4960], or Datagram Congestion Control Protocol (DCCP) [RFC4340], a range of ports can be, for example, 0-1023, 1024-65535, or 1024-49151.


target-protocol: A list of protocols involved in an attack. Values are taken from the IANA protocol registry [proto_numbers].

If ’target-protocol’ is not specified, then the request applies to any protocol.


target-fqdn: A list of Fully Qualified Domain Names (FQDNs) identifying resources under attack [RFC8499].

How a name is passed to an underlying name resolution library is implementation- and deployment-specific. Nevertheless, once the name is resolved into one or multiple IP addresses, DOTS servers MUST apply the same validation checks as those for ’target- prefix’.

The use of FQDNs may be suboptimal because:

* It induces both an extra load and increased delays on the DOTS server to handle and manage DNS resolution requests.

* It does not guarantee that the DOTS server will resolve a name to the same IP addresses that the DOTS client does.


target-uri: A list of Uniform Resource Identifiers (URIs) [RFC3986] identifying resources under attack.



The same validation checks used for ’target-fqdn’ MUST be followed by DOTS servers to validate a target URI.


alias-name: A list of aliases of resources for which the mitigation is requested. Aliases can be created using the DOTS data channel (Section 6.1 of [I-D.ietf-dots-data-channel]), direct configuration, or other means.

An alias is used in subsequent signal channel exchanges to refer more efficiently to the resources under attack.


lifetime: Lifetime of the mitigation request in seconds. The RECOMMENDED lifetime of a mitigation request is 3600 seconds -- this value was chosen to be long enough so that refreshing is not typically a burden on the DOTS client, while still making the request expire in a timely manner when the client has unexpectedly quit. DOTS clients MUST include this parameter in their mitigation requests. Upon the expiry of this lifetime, and if the request is not refreshed, the mitigation request is removed. The request can be refreshed by sending the same request again.

A lifetime of ’0’ in a mitigation request is an invalid value.

A lifetime of negative one (-1) indicates indefinite lifetime for the mitigation request. The DOTS server MAY refuse indefinite lifetime, for policy reasons; the granted lifetime value is returned in the response. DOTS clients MUST be prepared to not be granted mitigations with indefinite lifetimes.

The DOTS server MUST always indicate the actual lifetime in the response and the remaining lifetime in status messages sent to the DOTS client.


trigger-mitigation: If the parameter value is set to ’false’, DDoS mitigation will not be triggered for the mitigation request unless the DOTS signal channel session is lost.

If the DOTS client ceases to respond to heartbeat messages, the DOTS server can detect that the DOTS signal channel session is lost. More details are discussed in Section 4.7.



The default value of the parameter is ’true’ (that is, the mitigation starts immediately). If ’trigger-mitigation’ is not present in a request, this is equivalent to receiving a request with ’trigger-mitigation’ set to ’true’.


In deployments where server-domain DOTS gateways are enabled, identity information about the origin source client domain (’cdid’) SHOULD be propagated to the DOTS server. That information is meant to assist the DOTS server to enforce some policies such as grouping DOTS clients that belong to the same DOTS domain, limiting the number of DOTS requests, and identifying the mitigation scope. These policies can be enforced per-client, per-client domain, or both. Also, the identity information may be used for auditing and debugging purposes.

Figure 7 shows an example of a request relayed by a server-domain DOTS gateway.

Header: PUT (Code=0.03) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "mitigate" Uri-Path: "cdid=7eeaf349529eb55ed50113" Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw" Uri-Path: "mid=123" Content-Format: "application/dots+cbor"

{ ... }

Figure 7: PUT for DOTS Mitigation Request as Relayed by a DOTS Gateway

A server-domain DOTS gateway SHOULD add the following Uri-Path parameter:

cdid: Stands for Client Domain Identifier. The ’cdid’ is conveyed by a server-domain DOTS gateway to propagate the source domain identity from the gateway’s client-facing-side to the gateway’s server-facing-side, and from the gateway’s server-facing-side to the DOTS server. ’cdid’ may be used by the final DOTS server for policy enforcement purposes (e.g., enforce a quota on filtering rules). These policies are deployment-specific.



Server-domain DOTS gateways SHOULD support a configuration option to instruct whether ’cdid’ parameter is to be inserted.

In order to accommodate deployments that require enforcing per- client policies, per-client domain policies, or a combination thereof, server-domain DOTS gateways instructed to insert the ’cdid’ parameter MUST supply the SPKI hash of the DOTS client X.509 certificate, the DOTS client raw public key, or the hash of the "PSK identity" in the ’cdid’, following the same rules for generating the hash conveyed in ’cuid’, which is then used by the ultimate DOTS server to determine the corresponding client’s domain. The ’cdid’ generated by a server-domain gateway is likely to be the same as the ’cuid’ except if the DOTS message was relayed by a client-domain DOTS gateway or the ’cuid’ was generated from a rogue DOTS client.

If a DOTS client is provisioned, for example, with distinct certificates as a function of the peer server-domain DOTS gateway, distinct ’cdid’ values may be supplied by a server- domain DOTS gateway. The ultimate DOTS server MUST treat those ’cdid’ values as equivalent.

The ’cdid’ attribute MUST NOT be generated and included by DOTS clients.

DOTS servers MUST ignore ’cdid’ attributes that are directly supplied by source DOTS clients or client-domain DOTS gateways. This implies that first server-domain DOTS gateways MUST strip ’cdid’ attributes supplied by DOTS clients. DOTS servers SHOULD support a configuration parameter to identify DOTS gateways that are trusted to supply ’cdid’ attributes.

Only single-valued ’cdid’ are defined in this document. That is, only the first on-path server-domain DOTS gateway can insert a ’cdid’ value. This specification does not allow multiple server-domain DOTS gateways, whenever involved in the path, to insert a ’cdid’ value for each server-domain gateway.

This is an optional Uri-Path. When present, ’cdid’ MUST be positioned before ’cuid’.

A DOTS gateway SHOULD add the CoAP Hop-Limit Option [I-D.ietf-core-hop-limit].

Because of the complexity to handle partial failure cases, this specification does not allow for including multiple mitigation requests in the same PUT request. Concretely, a DOTS client MUST NOT



include multiple entries in the ’scope’ array of the same PUT request.

FQDN and URI mitigation scopes may be thought of as a form of scope alias, in which the addresses associated with the domain name or URI (as resolved by the DOTS server) represent the scope of the mitigation. Particularly, the IP addresses to which the host subcomponent of authority component of an URI resolves represent the ’target-prefix’, the URI scheme represents the ’target-protocol’, the port subcomponent of authority component of an URI represents the ’target-port-range’. If the optional port information is not present in the authority component, the default port defined for the URI scheme represents the ’target-port’.

In the PUT request at least one of the attributes ’target-prefix’, ’target-fqdn’,’target-uri’, or ’alias-name’ MUST be present.

Attributes and Uri-Path parameters with empty values MUST NOT be present in a request and render the entire request invalid.

Figure 8 shows a PUT request example to signal that TCP port numbers 80, 8080, and 443 used by 2001:db8:6401::1 and 2001:db8:6401::2 servers are under attack. The presence of ’cdid’ indicates that a server-domain DOTS gateway has modified the initial PUT request sent by the DOTS client. Note that ’cdid’ MUST NOT appear in the PUT request message body.



Header: PUT (Code=0.03) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "mitigate" Uri-Path: "cdid=7eeaf349529eb55ed50113" Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw" Uri-Path: "mid=123" Content-Format: "application/dots+cbor"

{ "ietf-dots-signal-channel:mitigation-scope": { "scope": [ { "target-prefix": [ "2001:db8:6401::1/128", "2001:db8:6401::2/128" ], "target-port-range": [ { "lower-port": 80 }, { "lower-port": 443 }, { "lower-port": 8080 } ], "target-protocol": [ 6 ], "lifetime": 3600 } ] } }

Figure 8: PUT for DOTS Mitigation Request (An Example)

The corresponding CBOR encoding format for the payload is shown in Figure 9.



A1 # map(1) 01 # unsigned(1) A1 # map(1) 02 # unsigned(2) 81 # array(1) A3 # map(3) 06 # unsigned(6) 82 # array(2) 74 # text(20) 323030313A6462383A363430313A3A312F313238 74 # text(20) 323030313A6462383A363430313A3A322F313238 07 # unsigned(7) 83 # array(3) A1 # map(1) 08 # unsigned(8) 18 50 # unsigned(80) A1 # map(1) 08 # unsigned(8) 19 01BB # unsigned(443) A1 # map(1) 08 # unsigned(8) 19 1F90 # unsigned(8080) 0A # unsigned(10) 81 # array(1) 06 # unsigned(6) 0E # unsigned(14) 19 0E10 # unsigned(3600)

Figure 9: PUT for DOTS Mitigation Request (CBOR)

In both DOTS signal and data channel sessions, the DOTS client MUST authenticate itself to the DOTS server (Section 8). The DOTS server MAY use the algorithm presented in Section 7 of [RFC7589] to derive the DOTS client identity or username from the client certificate. The DOTS client identity allows the DOTS server to accept mitigation requests with scopes that the DOTS client is authorized to manage.

The DOTS server couples the DOTS signal and data channel sessions using the DOTS client identity and optionally the ’cdid’ parameter value, so the DOTS server can validate whether the aliases conveyed in the mitigation request were indeed created by the same DOTS client using the DOTS data channel session. If the aliases were not created by the DOTS client, the DOTS server MUST return 4.00 (Bad Request) in the response.

The DOTS server couples the DOTS signal channel sessions using the DOTS client identity and optionally the ’cdid’ parameter value, and



the DOTS server uses ’mid’ and ’cuid’ Uri-Path parameter values to detect duplicate mitigation requests. If the mitigation request contains the ’alias-name’ and other parameters identifying the target resources (such as ’target-prefix’, ’target-port-range’, ’target- fqdn’, or ’target-uri’), the DOTS server appends the parameter values in ’alias-name’ with the corresponding parameter values in ’target- prefix’, ’target-port-range’, ’target-fqdn’, or ’target-uri’.

The DOTS server indicates the result of processing the PUT request using CoAP response codes. CoAP 2.xx codes are success. CoAP 4.xx codes are some sort of invalid requests (client errors). COAP 5.xx codes are returned if the DOTS server is in an error state or is currently unavailable to provide mitigation in response to the mitigation request from the DOTS client.

Figure 10 shows an example response to a PUT request that is successfully processed by a DOTS server (i.e., CoAP 2.xx response codes). This version of the specification forbids ’cuid’ and ’cdid’ (if used) to be returned in a response message body.

{ "ietf-dots-signal-channel:mitigation-scope": { "scope": [ { "mid": 123, "lifetime": 3600 } ] } }

Figure 10: 2.xx Response Body

If the request is missing a mandatory attribute, does not include ’cuid’ or ’mid’ Uri-Path options, includes multiple ’scope’ parameters, or contains invalid or unknown parameters, the DOTS server MUST reply with 4.00 (Bad Request). DOTS agents can safely ignore comprehension-optional parameters they don’t understand (Section 9.6.1.1).

A DOTS server that receives a mitigation request with a lifetime set to ’0’ MUST reply with a 4.00 (Bad Request).

If the DOTS server does not find the ’mid’ parameter value conveyed in the PUT request in its configuration data, it MAY accept the mitigation request by sending back a 2.01 (Created) response to the DOTS client; the DOTS server will consequently try to mitigate the attack. A DOTS server could reject mitigation requests when it is



near capacity or needs to rate-limit a particular client, for example.

The relative order of two mitigation requests, having the same ’trigger-mitigation’ type, from a DOTS client is determined by comparing their respective ’mid’ values. If two mitigation requests with the same ’trigger-mitigation’ type have overlapping mitigation scopes, the mitigation request with the highest numeric ’mid’ value will override the other mitigation request. Two mitigation requests from a DOTS client have overlapping scopes if there is a common IP address, IP prefix, FQDN, URI, or alias-name. To avoid maintaining a long list of overlapping mitigation requests (i.e., requests with the same ’trigger-mitigation’ type and overlapping scopes) from a DOTS client and avoid error-prone provisioning of mitigation requests from a DOTS client, the overlapped lower numeric ’mid’ MUST be automatically deleted and no longer available at the DOTS server. For example, if the DOTS server receives a mitigation request which overlaps with an existing mitigation with a higher numeric ’mid’, the DOTS server rejects the request by returning 4.09 (Conflict) to the DOTS client. The response includes enough information for a DOTS client to recognize the source of the conflict as described below in the ’conflict-information’ subtree with only the relevant nodes listed:

conflict-information: Indicates that a mitigation request is conflicting with another mitigation request. This optional attribute has the following structure:

conflict-cause: Indicates the cause of the conflict. The following values are defined:

1: Overlapping targets. ’conflict-scope’ provides more details about the conflicting target clauses.

conflict-scope: Characterizes the exact conflict scope. It may include a list of IP addresses, a list of prefixes, a list of port numbers, a list of target protocols, a list of FQDNs, a list of URIs, a list of alias-names, or a ’mid’.

If the DOTS server receives a mitigation request which overlaps with an active mitigation request, but both having distinct ’trigger- mitigation’ types, the DOTS server SHOULD deactivate (absent explicit policy/configuration otherwise) the mitigation request with ’trigger- mitigation’ set to false. Particularly, if the mitigation request with ’trigger-mitigation’ set to false is active, the DOTS server withdraws the mitigation request (i.e., status code is set to ’7’ as defined in Table 2) and transitions the status of the mitigation request to ’8’.



Upon DOTS signal channel session loss with a peer DOTS client, the DOTS server SHOULD withdraw (absent explicit policy/configuration otherwise) any active mitigation requests overlapping with mitigation requests having ’trigger-mitigation’ set to false from that DOTS client, as the loss of the session implicitly activates these preconfigured mitigation requests and they take precedence. Note that active-but-terminating period is not observed for mitigations withdrawn at the initiative of the DOTS server.

DOTS clients may adopt various strategies for setting the scopes of immediate and pre-configured mitigation requests to avoid potential conflicts. For example, a DOTS client may tweak pre-configured scopes so that the scope of any overlapping immediate mitigation request will be a subset of the pre-configured scopes. Also, if an immediate mitigation request overlaps with any of the pre-configured scopes, the DOTS client sets the scope of the overlapping immediate mitigation request to be a subset of the pre-configured scopes, so as to get a broad mitigation when the DOTS signal channel collapses and maximize the chance of recovery.

If the request is conflicting with an existing mitigation request from a different DOTS client, the DOTS server may return 2.01 (Created) or 4.09 (Conflict) to the requesting DOTS client. If the DOTS server decides to maintain the new mitigation request, the DOTS server returns 2.01 (Created) to the requesting DOTS client. If the DOTS server decides to reject the new mitigation request, the DOTS server returns 4.09 (Conflict) to the requesting DOTS client. For both 2.01 (Created) and 4.09 (Conflict) responses, the response includes enough information for a DOTS client to recognize the source of the conflict as described below:

conflict-information: Indicates that a mitigation request is conflicting with another mitigation request(s) from other DOTS client(s). This optional attribute has the following structure:

conflict-status: Indicates the status of a conflicting mitigation request. The following values are defined:

1: DOTS server has detected conflicting mitigation requests from different DOTS clients. This mitigation request is currently inactive until the conflicts are resolved. Another mitigation request is active.

2: DOTS server has detected conflicting mitigation requests from different DOTS clients. This mitigation request is currently active.



3: DOTS server has detected conflicting mitigation requests from different DOTS clients. All conflicting mitigation requests are inactive.

conflict-cause: Indicates the cause of the conflict. The following values are defined:

1: Overlapping targets. ’conflict-scope’ provides more details about the conflicting target clauses.

2: Conflicts with an existing accept-list. This code is returned when the DDoS mitigation detects source addresses/ prefixes in the accept-listed ACLs are attacking the target.

3: CUID Collision. This code is returned when a DOTS client uses a ’cuid’ that is already used by another DOTS client. This code is an indication that the request has been rejected and a new request with a new ’cuid’ is to be re- sent by the DOTS client (see the example shown in Figure 11). Note that ’conflict-status’, ’conflict-scope’, and ’retry-timer’ MUST NOT be returned in the error response.

conflict-scope: Characterizes the exact conflict scope. It may include a list of IP addresses, a list of prefixes, a list of port numbers, a list of target protocols, a list of FQDNs, a list of URIs, a list of alias-names, or references to conflicting ACLs (by an ’acl-name’, typically [I-D.ietf-dots-data-channel]).

retry-timer: Indicates, in seconds, the time after which the DOTS client may re-issue the same request. The DOTS server returns ’retry-timer’ only to DOTS client(s) for which a mitigation request is deactivated. Any retransmission of the same mitigation request before the expiry of this timer is likely to be rejected by the DOTS server for the same reasons.

The retry-timer SHOULD be equal to the lifetime of the active mitigation request resulting in the deactivation of the conflicting mitigation request.

If the DOTS server decides to maintain a state for the deactivated mitigation request, the DOTS server updates the lifetime of the deactivated mitigation request to ’retry-timer + 45 seconds’ (that is, this mitigation request remains deactivated for the entire duration of ’retry-timer + 45 seconds’) so that the DOTS client can refresh the deactivated



mitigation request after ’retry-timer’ seconds, but before the expiry of the lifetime, and check if the conflict is resolved.

Header: PUT (Code=0.03) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "mitigate" Uri-Path: "cuid=7eeaf349529eb55ed50113" Uri-Path: "mid=12"

(1) Request with a conflicting ’cuid’

{ "ietf-dots-signal-channel:mitigation-scope": { "scope": [ { "conflict-information": { "conflict-cause": "cuid-collision" } } ] } }

(2) Message body of the 4.09 (Conflict) response from the DOTS server

Header: PUT (Code=0.03) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "mitigate" Uri-Path: "cuid=f30d281ce6b64fc5a0b91e" Uri-Path: "mid=12"

(3) Request with a new ’cuid’

Figure 11: Example of Generating a New ’cuid’

As an active attack evolves, DOTS clients can adjust the scope of requested mitigation as necessary, by refining the scope of resources requiring mitigation. This can be achieved by sending a PUT request with a new ’mid’ value that will override the existing one with overlapping mitigation scopes.

For a mitigation request to continue beyond the initial negotiated lifetime, the DOTS client has to refresh the current mitigation request by sending a new PUT request. This PUT request MUST use the same ’mid’ value, and MUST repeat all the other parameters as sent in



the original mitigation request apart from a possible change to the lifetime parameter value. In such case, the DOTS server MAY update the mitigation request, and a 2.04 (Changed) response is returned to indicate a successful update of the mitigation request. If this is not the case, the DOTS server MUST reject the request with a 4.00 (Bad Request).

4.4.2. Retrieve Information Related to a Mitigation

A GET request is used by a DOTS client to retrieve information (including status) of DOTS mitigations from a DOTS server.

’cuid’ is a mandatory Uri-Path parameter for GET requests.

Uri-Path parameters with empty values MUST NOT be present in a request.

The same considerations for manipulating ’cdid’ parameter by server- domain DOTS gateways specified in Section 4.4.1 MUST be followed for GET requests.

The ’c’ Uri-Query option is used to control selection of configuration and non-configuration data nodes. Concretely, the ’c’ (content) parameter and its permitted values defined in the following table [I-D.ietf-core-comi] can be used to retrieve non-configuration data (attack mitigation status), configuration data, or both. The DOTS server MAY support this optional filtering capability. It can safely ignore it if not supported. If the DOTS client supports the optional filtering capability, it SHOULD use "c=n" query (to get back only the dynamically changing data) or "c=c" query (to get back the static configuration values) when the DDoS attack is active to limit the size of the response.

+-------+-----------------------------------------------------+ | Value | Description | +-------+-----------------------------------------------------+ | c | Return only configuration descendant data nodes | | n | Return only non-configuration descendant data nodes | | a | Return all descendant data nodes | +-------+-----------------------------------------------------+

The DOTS client can use Block-wise transfer [RFC7959] to get the list of all its mitigations maintained by a DOTS server, it can send Block2 Option in a GET request with NUM = 0 to aid in limiting the size of the response. If the representation of all the active mitigation requests associated with the DOTS client does not fit within a single datagram, the DOTS server MUST use the Block2 Option with NUM = 0 in the GET response. The Size2 Option may be conveyed



in the response to indicate the total size of the resource representation. The DOTS client retrieves the rest of the representation by sending additional GET requests with Block2 Options containing NUM values greater than zero. The DOTS client MUST adhere to the block size preferences indicated by the DOTS server in the response. If the DOTS server uses the Block2 Option in the GET response and the response is for a dynamically changing resource (e.g., "c=n" or "c=a" query), the DOTS server MUST include the ETag Option in the response. The DOTS client MUST include the same ETag value in subsequent GET requests to retrieve the rest of the representation.

The following examples illustrate how a DOTS client retrieves active mitigation requests from a DOTS server. In particular:

o Figure 12 shows the example of a GET request to retrieve all DOTS mitigation requests signaled by a DOTS client.

o Figure 13 shows the example of a GET request to retrieve a specific DOTS mitigation request signaled by a DOTS client. The configuration data to be reported in the response is formatted in the same order as was processed by the DOTS server in the original mitigation request.

These two examples assume the default of "c=a"; that is, the DOTS client asks for all data to be reported by the DOTS server.

Header: GET (Code=0.01) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "mitigate" Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw" Observe: 0

Figure 12: GET to Retrieve all DOTS Mitigation Requests

Header: GET (Code=0.01) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "mitigate" Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw" Uri-Path: "mid=12332" Observe: 0

Figure 13: GET to Retrieve a Specific DOTS Mitigation Request

If the DOTS server does not find the ’mid’ Uri-Path value conveyed in the GET request in its configuration data for the requesting DOTS



client, it MUST respond with a 4.04 (Not Found) error response code. Likewise, the same error MUST be returned as a response to a request to retrieve all mitigation records (i.e., ’mid’ Uri-Path is not defined) of a given DOTS client if the DOTS server does not find any mitigation record for that DOTS client. As a reminder, a DOTS client is identified by its identity (e.g., client certificate, ’cuid’) and optionally the ’cdid’.

Figure 14 shows a response example of all active mitigation requests associated with the DOTS client as maintained by the DOTS server. The response indicates the mitigation status of each mitigation request.



{ "ietf-dots-signal-channel:mitigation-scope": { "scope": [ { "mid": 12332, "mitigation-start": "1507818434", "target-prefix": [ "2001:db8:6401::1/128", "2001:db8:6401::2/128" ], "target-protocol": [ 17 ], "lifetime": 1756, "status": "attack-successfully-mitigated", "bytes-dropped": "134334555", "bps-dropped": "43344", "pkts-dropped": "333334444", "pps-dropped": "432432" }, { "mid": 12333, "mitigation-start": "1507818393", "target-prefix": [ "2001:db8:6401::1/128", "2001:db8:6401::2/128" ], "target-protocol": [ 6 ], "lifetime": 1755, "status": "attack-stopped", "bytes-dropped": "0", "bps-dropped": "0", "pkts-dropped": "0", "pps-dropped": "0" } ] } }

Figure 14: Response Body to a GET Request

The mitigation status parameters are described below:

mitigation-start: Mitigation start time is expressed in seconds relative to 1970-01-01T00:00Z in UTC time (Section 2.4.1 of



[RFC7049]). The CBOR encoding is modified so that the leading tag 1 (epoch-based date/time) MUST be omitted.

This is a mandatory attribute when an attack mitigation is active. Particularly, ’mitigation-start’ is not returned for a mitigation with ’status’ code set to 8.

lifetime: The remaining lifetime of the mitigation request, in seconds.


status: Status of attack mitigation. The various possible values of ’status’ parameter are explained in Table 2.


bytes-dropped: The total dropped byte count for the mitigation request since the attack mitigation is triggered. The count wraps around when it reaches the maximum value of unsigned integer64.


bps-dropped: The average number of dropped bytes per second for the mitigation request since the attack mitigation is triggered. This average SHOULD be over five-minute intervals (that is, measuring bytes into five-minute buckets and then averaging these buckets over the time since the mitigation was triggered).


pkts-dropped: The total number of dropped packet count for the mitigation request since the attack mitigation is triggered. The count wraps around when it reaches the maximum value of unsigned integer64.


pps-dropped: The average number of dropped packets per second for the mitigation request since the attack mitigation is triggered. This average SHOULD be over five-minute intervals (that is, measuring packets into five-minute buckets and then averaging these buckets over the time since the mitigation was triggered).




+-----------+-------------------------------------------------------+ | Parameter | Description | | Value | | +-----------+-------------------------------------------------------+ | 1 | Attack mitigation setup is in progress (e.g., | | | changing the network path to redirect the inbound | | | traffic to a DOTS mitigator). | +-----------+-------------------------------------------------------+ | 2 | Attack is being successfully mitigated (e.g., traffic | | | is redirected to a DDoS mitigator and attack traffic | | | is dropped). | +-----------+-------------------------------------------------------+ | 3 | Attack has stopped and the DOTS client can withdraw | | | the mitigation request. This status code will be | | | transmitted for immediate mitigation requests till | | | the mitigation is withdrawn or the lifetime expires. | | | For mitigation requests with pre-configured scopes | | | (i.e., ’trigger-mitigation’ set to ’false’), this | | | status code will be transmitted 4 times and then | | | transition to "8". | +-----------+-------------------------------------------------------+ | 4 | Attack has exceeded the mitigation provider | | | capability. | +-----------+-------------------------------------------------------+ | 5 | DOTS client has withdrawn the mitigation request and | | | the mitigation is active but terminating. | +-----------+-------------------------------------------------------+ | 6 | Attack mitigation is now terminated. | +-----------+-------------------------------------------------------+ | 7 | Attack mitigation is withdrawn (by the DOTS server). | | | If a mitigation request with ’trigger-mitigation’ set | | | to false is withdrawn because it overlaps with an | | | immediate mitigation request, this status code will | | | be transmitted 4 times and then transition to "8" for | | | the mitigation request with pre-configured scopes. | +-----------+-------------------------------------------------------+ | 8 | Attack mitigation will be triggered for the | | | mitigation request only when the DOTS signal channel | | | session is lost. | +-----------+-------------------------------------------------------+

Table 2: Values of ’status’ Parameter

4.4.2.1. DOTS Servers Sending Mitigation Status

The Observe Option defined in [RFC7641] extends the CoAP core protocol with a mechanism for a CoAP client to "observe" a resource on a CoAP server: The client retrieves a representation of the



resource and requests this representation be updated by the server as long as the client is interested in the resource. DOTS implementations MUST use the Observe Option for both ’mitigate’ and ’config’ (Section 4.2).

A DOTS client conveys the Observe Option set to ’0’ in the GET request to receive asynchronous notifications of attack mitigation status from the DOTS server.

Unidirectional mitigation notifications within the bidirectional signal channel enables asynchronous notifications between the agents. [RFC7641] indicates that (1) a notification can be sent in a Confirmable or a Non-confirmable message, and (2) the message type used is typically application-dependent and may be determined by the server for each notification individually. For DOTS server application, the message type MUST always be set to Non-confirmable even if the underlying COAP library elects a notification to be sent in a Confirmable message. This overrides the behavior defined in Section 4.5 of [RFC7641] to send a Confirmable message instead of a Non-confirmable message at least every 24 hour for the following reasons: First, the DOTS signal channel uses a heartbeat mechanism to determine if the DOTS client is alive. Second, Confirmable messages are not suitable during an attack.

Due to the higher likelihood of packet loss during a DDoS attack, the DOTS server periodically sends attack mitigation status to the DOTS client and also notifies the DOTS client whenever the status of the attack mitigation changes. If the DOTS server cannot maintain an RTT estimate, it MUST NOT send more than one asynchronous notification every 3 seconds, and SHOULD use an even less aggressive rate whenever possible (case 2 in Section 3.1.3 of [RFC8085]).

When conflicting requests are detected, the DOTS server enforces the corresponding policy (e.g., accept all requests, reject all requests, accept only one request but reject all the others, ...). It is assumed that this policy is supplied by the DOTS server administrator or it is a default behavior of the DOTS server implementation. Then, the DOTS server sends notification message(s) to the DOTS client(s) at the origin of the conflict (refer to the conflict parameters defined in Section 4.4.1). A conflict notification message includes information about the conflict cause, scope, and the status of the mitigation request(s). For example,

o A notification message with ’status’ code set to ’7 (Attack mitigation is withdrawn)’ and ’conflict-status’ set to ’1’ is sent to a DOTS client to indicate that an active mitigation request is deactivated because a conflict is detected.



o A notification message with ’status’ code set to ’1 (Attack mitigation is in progress)’ and ’conflict-status’ set to ’2’ is sent to a DOTS client to indicate that this mitigation request is in progress, but a conflict is detected.

Upon receipt of a conflict notification message indicating that a mitigation request is deactivated because of a conflict, a DOTS client MUST NOT resend the same mitigation request before the expiry of ’retry-timer’. It is also recommended that DOTS clients support means to alert administrators about mitigation conflicts.

A DOTS client that is no longer interested in receiving notifications from the DOTS server can simply "forget" the observation. When the DOTS server sends the next notification, the DOTS client will not recognize the token in the message and thus will return a Reset message. This causes the DOTS server to remove the associated entry. Alternatively, the DOTS client can explicitly deregister itself by issuing a GET request that has the Token field set to the token of the observation to be cancelled and includes an Observe Option with the value set to ’1’ (deregister). The latter is more deterministic and thus is RECOMMENDED.

Figure 15 shows an example of a DOTS client requesting a DOTS server to send notifications related to a mitigation request. Note that for mitigations with pre-configured scopes (i.e., ’trigger-mitigation’ set to ’false’), the state will need to transition from 3 (attack- stopped) to 8 (attack-mitigation-signal-loss).



+-----------+ +-----------+ |DOTS client| |DOTS server| +-----------+ +-----------+ | | | GET /<mid> | | Token: 0x4a | Registration | Observe: 0 | +----------------------------------------->| | | | 2.05 Content | | Token: 0x4a | Notification of | Observe: 12 | the current state | status: "attack-mitigation-in-progress" | | | |<-----------------------------------------+ | 2.05 Content | | Token: 0x4a | Notification upon | Observe: 44 | a state change | status: "attack-successfully-mitigated" | | | |<-----------------------------------------+ | 2.05 Content | | Token: 0x4a | Notification upon | Observe: 60 | a state change | status: "attack-stopped" | |<-----------------------------------------+ | | ...

Figure 15: Notifications of Attack Mitigation Status

4.4.2.2. DOTS Clients Polling for Mitigation Status

The DOTS client can send the GET request at frequent intervals without the Observe Option to retrieve the configuration data of the mitigation request and non-configuration data (i.e., the attack status). DOTS clients MAY be configured with a policy indicating the frequency of polling DOTS servers to get the mitigation status. This frequency MUST NOT be more than one UDP datagram per RTT as discussed in Section 3.1.3 of [RFC8085].

If the DOTS server has been able to mitigate the attack and the attack has stopped, the DOTS server indicates as such in the status. In such case, the DOTS client recalls the mitigation request by issuing a DELETE request for this mitigation request (Section 4.4.4).

A DOTS client SHOULD react to the status of the attack as per the information sent by the DOTS server rather than performing its own



detection that the attack has been mitigated. This ensures that the DOTS client does not recall a mitigation request prematurely because it is possible that the DOTS client does not sense the DDoS attack on its resources, but the DOTS server could be actively mitigating the attack because the attack is not completely averted.

4.4.3. Efficacy Update from DOTS Clients

While DDoS mitigation is in progress, due to the likelihood of packet loss, a DOTS client MAY periodically transmit DOTS mitigation efficacy updates to the relevant DOTS server. A PUT request is used to convey the mitigation efficacy update to the DOTS server. This PUT request is treated as a refresh of the current mitigation.

The PUT request used for efficacy update MUST include all the parameters used in the PUT request to carry the DOTS mitigation request (Section 4.4.1) unchanged apart from the ’lifetime’ parameter value. If this is not the case, the DOTS server MUST reject the request with a 4.00 (Bad Request).

The If-Match Option (Section 5.10.8.1 of [RFC7252]) with an empty value is used to make the PUT request conditional on the current existence of the mitigation request. If UDP is used as transport, CoAP requests may arrive out-of-order. For example, the DOTS client may send a PUT request to convey an efficacy update to the DOTS server followed by a DELETE request to withdraw the mitigation request, but the DELETE request arrives at the DOTS server before the PUT request. To handle out-of-order delivery of requests, if an If- Match Option is present in the PUT request and the ’mid’ in the request matches a mitigation request from that DOTS client, the request is processed by the DOTS server. If no match is found, the PUT request is silently ignored by the DOTS server.

An example of an efficacy update message, which includes an If-Match Option with an empty value, is depicted in Figure 16.



Header: PUT (Code=0.03) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "mitigate" Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw" Uri-Path: "mid=123" If-Match: Content-Format: "application/dots+cbor"

{ "ietf-dots-signal-channel:mitigation-scope": { "scope": [ { "target-prefix": [ "2001:db8:6401::1/128", "2001:db8:6401::2/128" ], "target-port-range": [ { "lower-port": 80 }, { "lower-port": 443 }, { "lower-port": 8080 } ], "target-protocol": [ 6 ], "attack-status": "under-attack" } ] } }

Figure 16: An Example of Efficacy Update

The ’attack-status’ parameter is a mandatory attribute when performing an efficacy update. The various possible values contained in the ’attack-status’ parameter are described in Table 3.



+-----------+-------------------------------------------------------+ | Parameter | Description | | value | | +-----------+-------------------------------------------------------+ | 1 | The DOTS client determines that it is still under | | | attack. | +-----------+-------------------------------------------------------+ | 2 | The DOTS client determines that the attack is | | | successfully mitigated (e.g., attack traffic is not | | | seen). | +-----------+-------------------------------------------------------+

Table 3: Values of ’attack-status’ Parameter

The DOTS server indicates the result of processing a PUT request using CoAP response codes. The response code 2.04 (Changed) is returned if the DOTS server has accepted the mitigation efficacy update. The error response code 5.03 (Service Unavailable) is returned if the DOTS server has erred or is incapable of performing the mitigation. As specified in [RFC7252], 5.03 uses Max-Age option to indicate the number of seconds after which to retry.

4.4.4. Withdraw a Mitigation

DELETE requests are used to withdraw DOTS mitigation requests from DOTS servers (Figure 17).

’cuid’ and ’mid’ are mandatory Uri-Path parameters for DELETE requests.

The same considerations for manipulating ’cdid’ parameter by DOTS gateways, as specified in Section 4.4.1, MUST be followed for DELETE requests. Uri-Path parameters with empty values MUST NOT be present in a request.

Header: DELETE (Code=0.04) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "mitigate" Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw" Uri-Path: "mid=123"

Figure 17: Withdraw a DOTS Mitigation

If the DELETE request does not include ’cuid’ and ’mid’ parameters, the DOTS server MUST reply with a 4.00 (Bad Request).



Once the request is validated, the DOTS server immediately acknowledges a DOTS client’s request to withdraw the DOTS signal using 2.02 (Deleted) response code with no response payload. A 2.02 (Deleted) Response Code is returned even if the ’mid’ parameter value conveyed in the DELETE request does not exist in its configuration data before the request.

If the DOTS server finds the ’mid’ parameter value conveyed in the DELETE request in its configuration data for the DOTS client, then to protect against route or DNS flapping caused by a DOTS client rapidly removing a mitigation, and to dampen the effect of oscillating attacks, the DOTS server MAY allow mitigation to continue for a limited period after acknowledging a DOTS client’s withdrawal of a mitigation request. During this period, the DOTS server status messages SHOULD indicate that mitigation is active but terminating (Section 4.4.2).

The initial active-but-terminating period SHOULD be sufficiently long to absorb latency incurred by route propagation. The active-but- terminating period SHOULD be set by default to 120 seconds. If the client requests mitigation again before the initial active-but- terminating period elapses, the DOTS server MAY exponentially increase (the base of the exponent is 2) the active-but-terminating period up to a maximum of 300 seconds (5 minutes).

Once the active-but-terminating period elapses, the DOTS server MUST treat the mitigation as terminated, as the DOTS client is no longer responsible for the mitigation.

If a mitigation is triggered due to a signal channel loss, the DOTS server relies upon normal triggers to stop that mitigation (typically, receipt of a valid DELETE request, expiry of the mitigation lifetime, or scrubbing the traffic to the attack target). In particular, the DOTS server MUST NOT consider the signal channel recovery as a trigger to stop the mitigation.

4.5. DOTS Signal Channel Session Configuration

A DOTS client can negotiate, configure, and retrieve the DOTS signal channel session behavior with its DOTS peers. The DOTS signal channel can be used, for example, to configure the following:

a. Heartbeat interval (heartbeat-interval): DOTS agents regularly send heartbeats to each other after mutual authentication is successfully completed in order to keep the DOTS signal channel open. Heartbeat messages are exchanged between DOTS agents every ’heartbeat-interval’ seconds to detect the current status of the DOTS signal channel session.



b. Missing heartbeats allowed (missing-hb-allowed): This variable indicates the maximum number of consecutive heartbeat messages for which a DOTS agent did not receive a response before concluding that the session is disconnected or defunct.

c. Acceptable probing rate (probing-rate): This parameter indicates the average data rate that must not be exceeded by a DOTS agent in sending to a peer DOTS agent that does not respond.

d. Acceptable signal loss ratio: Maximum retransmissions, retransmission timeout value, and other message transmission parameters for Confirmable messages over the DOTS signal channel.

When the DOTS signal channel is established over a reliable transport (e.g., TCP), there is no need for the reliability mechanisms provided by CoAP over UDP since the underlying TCP connection provides retransmissions and deduplication [RFC8323]. As a reminder, CoAP over reliable transports does not support Confirmable or Non- confirmable message types. As such, the transmission-related parameters (missing-hb-allowed and acceptable signal loss ratio) are negotiated only for DOTS over unreliable transports.

The same or distinct configuration sets may be used during times when a mitigation is active (’mitigating-config’) and when no mitigation is active (’idle-config’). This is particularly useful for DOTS servers that might want to reduce heartbeat frequency or cease heartbeat exchanges when an active DOTS client has not requested mitigation. If distinct configurations are used, DOTS agents MUST follow the appropriate configuration set as a function of the mitigation activity (e.g., if no mitigation request is active (also referred to as ’idle’ time), ’idle-config’-related values must be followed). Additionally, DOTS agents MUST automatically switch to the other configuration upon a change in the mitigation activity (e.g., if an attack mitigation is launched after an ’idle’ time, the DOTS agent switches from ’idle-config’ to ’mitigating-config’-related values).

CoAP Requests and responses are indicated for reliable delivery by marking them as Confirmable messages. DOTS signal channel session configuration requests and responses are marked as Confirmable messages. As explained in Section 2.1 of [RFC7252], a Confirmable message is retransmitted using a default timeout and exponential back-off between retransmissions, until the DOTS server sends an Acknowledgement message (ACK) with the same Message ID conveyed from the DOTS client.

Message transmission parameters are defined in Section 4.8 of [RFC7252]. The DOTS server can either piggyback the response in the



acknowledgement message or, if the DOTS server cannot respond immediately to a request carried in a Confirmable message, it simply responds with an Empty Acknowledgement message so that the DOTS client can stop retransmitting the request. Empty Acknowledgement messages are explained in Section 2.2 of [RFC7252]. When the response is ready, the server sends it in a new Confirmable message which in turn needs to be acknowledged by the DOTS client (see Sections 5.2.1 and 5.2.2 of [RFC7252]). Requests and responses exchanged between DOTS agents during ’idle’ time, except heartbeat messages, are marked as Confirmable messages.

Implementation Note: A DOTS client that receives a response in a Confirmable message may want to clean up the message state right after sending the ACK. If that ACK is lost and the DOTS server retransmits the Confirmable message, the DOTS client may no longer have any state that would help it correlate this response: from the DOTS client’s standpoint, the retransmission message is unexpected. The DOTS client will send a Reset message so it does not receive any more retransmissions. This behavior is normal and not an indication of an error (see Section 5.3.2 of [RFC7252] for more details).

4.5.1. Discover Configuration Parameters

A GET request is used to obtain acceptable (e.g., minimum and maximum values) and current configuration parameters on the DOTS server for DOTS signal channel session configuration. This procedure occurs between a DOTS client and its immediate peer DOTS server. As such, this GET request MUST NOT be relayed by a DOTS gateway.

Figure 18 shows how to obtain configuration parameters that the DOTS server will find acceptable.

Header: GET (Code=0.01) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "config"

Figure 18: GET to Retrieve Configuration

The DOTS server in the 2.05 (Content) response conveys the current, minimum, and maximum attribute values acceptable by the DOTS server (Figure 19).

{ "ietf-dots-signal-channel:signal-config": { "mitigating-config": { "heartbeat-interval": {



"max-value": number, "min-value": number, "current-value": number }, "missing-hb-allowed": { "max-value": number, "min-value": number, "current-value": number }, "probing-rate": { "max-value": number, "min-value": number, "current-value": number }, "max-retransmit": { "max-value": number, "min-value": number, "current-value": number }, "ack-timeout": { "max-value-decimal": "string", "min-value-decimal": "string", "current-value-decimal": "string" }, "ack-random-factor": { "max-value-decimal": "string", "min-value-decimal": "string", "current-value-decimal": "string" } }, "idle-config": { "heartbeat-interval": { "max-value": number, "min-value": number, "current-value": number }, "missing-hb-allowed": { "max-value": number, "min-value": number, "current-value": number }, "probing-rate": { "max-value": number, "min-value": number, "current-value": number }, "max-retransmit": { "max-value": number,



"min-value": number, "current-value": number }, "ack-timeout": { "max-value-decimal": "string", "min-value-decimal": "string", "current-value-decimal": "string" }, "ack-random-factor": { "max-value-decimal": "string", "min-value-decimal": "string", "current-value-decimal": "string" } } } }

Figure 19: GET Configuration Response Body Schema

The parameters in Figure 19 are described below:

mitigating-config: Set of configuration parameters to use when a mitigation is active. The following parameters may be included:

heartbeat-interval: Time interval in seconds between two consecutive heartbeat messages.

’0’ is used to disable the heartbeat mechanism.


missing-hb-allowed: Maximum number of consecutive heartbeat messages for which the DOTS agent did not receive a response before concluding that the session is disconnected.


probing-rate: The average data rate that must not be exceeded by a DOTS agent in sending to a peer DOTS agent that does not respond (referred to as PROBING_RATE parameter in CoAP).


max-retransmit: Maximum number of retransmissions for a message (referred to as MAX_RETRANSMIT parameter in CoAP).




ack-timeout: Timeout value in seconds used to calculate the initial retransmission timeout value (referred to as ACK_TIMEOUT parameter in CoAP).


ack-random-factor: Random factor used to influence the timing of retransmissions (referred to as ACK_RANDOM_FACTOR parameter in CoAP).


idle-config: Set of configuration parameters to use when no mitigation is active. This attribute has the same structure as ’mitigating-config’.

Figure 20 shows an example of acceptable and current configuration parameters on a DOTS server for DOTS signal channel session configuration. The same acceptable configuration is used during mitigation and idle times.

{ "ietf-dots-signal-channel:signal-config": { "mitigating-config": { "heartbeat-interval": { "max-value": 240, "min-value": 15, "current-value": 30 }, "missing-hb-allowed": { "max-value": 20, "min-value": 3, "current-value": 15 }, "probing-rate": { "max-value": 20, "min-value": 5, "current-value": 15 }, "max-retransmit": { "max-value": 15, "min-value": 2, "current-value": 3 }, "ack-timeout": { "max-value-decimal": "30.00", "min-value-decimal": "1.00", "current-value-decimal": "2.00"



}, "ack-random-factor": { "max-value-decimal": "4.00", "min-value-decimal": "1.10", "current-value-decimal": "1.50" } }, "idle-config": { "heartbeat-interval": { "max-value": 240, "min-value": 15, "current-value": 30 }, "missing-hb-allowed": { "max-value": 20, "min-value": 3, "current-value": 15 }, "probing-rate": { "max-value": 20, "min-value": 5, "current-value": 15 }, "max-retransmit": { "max-value": 15, "min-value": 2, "current-value": 3 }, "ack-timeout": { "max-value-decimal": "30.00", "min-value-decimal": "1.00", "current-value-decimal": "2.00" }, "ack-random-factor": { "max-value-decimal": "4.00", "min-value-decimal": "1.10", "current-value-decimal": "1.50" } } } }

Figure 20: Example of a Configuration Response Body



4.5.2. Convey DOTS Signal Channel Session Configuration

A PUT request (Figures 21 and 22) is used to convey the configuration parameters for the signal channel (e.g., heartbeat interval, maximum retransmissions). Message transmission parameters for CoAP are defined in Section 4.8 of [RFC7252]. The RECOMMENDED values of transmission parameter values are ack-timeout (2 seconds), max- retransmit (3), and ack-random-factor (1.5). In addition to those parameters, the RECOMMENDED specific DOTS transmission parameter values are ’heartbeat-interval’ (30 seconds) and ’missing-hb-allowed’ (15).

Note: heartbeat-interval should be tweaked to also assist DOTS messages for NAT traversal (SIG-011 of [RFC8612]). According to [RFC8085], heartbeat messages must not be sent more frequently than once every 15 seconds and should use longer intervals when possible. Furthermore, [RFC4787] recommends NATs to use a state timeout of 2 minutes or longer, but experience shows that sending packets every 15 to 30 seconds is necessary to prevent the majority of middleboxes from losing state for UDP flows. From that standpoint, the RECOMMENDED minimum heartbeat-interval is 15 seconds and the RECOMMENDED maximum heartbeat-interval is 240 seconds. The recommended value of 30 seconds is selected to anticipate the expiry of NAT state.

A heartbeat-interval of 30 seconds may be considered as too chatty in some deployments. For such deployments, DOTS agents may negotiate longer heartbeat-interval values to prevent any network overload with too frequent heartbeats.

Different heartbeat intervals can be defined for ’mitigating- config’ and ’idle-config’ to reduce being too chatty during idle times. If there is an on-path translator between the DOTS client (standalone or part of a DOTS gateway) and the DOTS server, the ’mitigating-config’ heartbeat-interval has to be smaller than the translator session timeout. It is recommended that the ’idle- config’ heartbeat-interval is also smaller than the translator session timeout to prevent translator traversal issues, or disabled entirely. Means to discover the lifetime assigned by a translator are out of scope.

Given that the size of the heartbeat request can not exceed (heartbeat-interval * probing-rate) bytes, probing-rate should be set appropriately to avoid slowing down heartbeat exchanges. For example, probing-rate may be set to 2 * ("size of encrypted DOTS heartbeat request"/heartbeat-interval) or (("size of encrypted DOTS heartbeat request" + "average size of an encrypted mitigation request")/heartbeat-interval). Absent any explicit configuration



or inability to dynamically adjust probing-rate values (Section 4.8.1 of [RFC7252]), DOTS agents use 5 bytes/second as a default probing-rate value.

If the DOTS agent wishes to change the default values of message transmission parameters, it SHOULD follow the guidance given in Section 4.8.1 of [RFC7252]. The DOTS agents MUST use the negotiated values for message transmission parameters and default values for non-negotiated message transmission parameters.

The signal channel session configuration is applicable to a single DOTS signal channel session between DOTS agents, so the ’cuid’ Uri- Path MUST NOT be used.

Header: PUT (Code=0.03) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "config" Uri-Path: "sid=123" Content-Format: "application/dots+cbor"

{ ... }

Figure 21: PUT to Convey the DOTS Signal Channel Session Configuration Data

The additional Uri-Path parameter to those defined in Table 1 is as follows:

sid: Session Identifier is an identifier for the DOTS signal channel session configuration data represented as an integer. This identifier MUST be generated by DOTS clients. ’sid’ values MUST increase monotonically (when a new PUT is generated by a DOTS client to convey the configuration parameters for the signal channel).




{ "ietf-dots-signal-channel:signal-config": { "mitigating-config": { "heartbeat-interval": { "current-value": number }, "missing-hb-allowed": { "current-value": number }, "probing-rate": { "current-value": number }, "max-retransmit": { "current-value": number }, "ack-timeout": { "current-value-decimal": "string" }, "ack-random-factor": { "current-value-decimal": "string" } }, "idle-config": { "heartbeat-interval": { "current-value": number }, "missing-hb-allowed": { "current-value": number }, "probing-rate": { "current-value": number }, "max-retransmit": { "current-value": number }, "ack-timeout": { "current-value-decimal": "string" }, "ack-random-factor": { "current-value-decimal": "string" } } } }

Figure 22: PUT to Convey the DOTS Signal Channel Session Configuration Data (Message Body Schema)



The meaning of the parameters in the CBOR body (Figure 22) is defined in Section 4.5.1.

At least one of the attributes ’heartbeat-interval’, ’missing-hb- allowed’, ’probing-rate’, ’max-retransmit’, ’ack-timeout’, and ’ack- random-factor’ MUST be present in the PUT request. Note that ’heartbeat-interval’, ’missing-hb-allowed’, ’probing-rate’, ’max- retransmit’, ’ack-timeout’, and ’ack-random-factor’, if present, do not need to be provided for both ’mitigating-config’, and ’idle- config’ in a PUT request.

The PUT request with a higher numeric ’sid’ value overrides the DOTS signal channel session configuration data installed by a PUT request with a lower numeric ’sid’ value. To avoid maintaining a long list of ’sid’ requests from a DOTS client, the lower numeric ’sid’ MUST be automatically deleted and no longer available at the DOTS server.

Figure 23 shows a PUT request example to convey the configuration parameters for the DOTS signal channel. In this example, the heartbeat mechanism is disabled when no mitigation is active, while the heartbeat interval is set to ’30’ when a mitigation is active.



Header: PUT (Code=0.03) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "config" Uri-Path: "sid=123" Content-Format: "application/dots+cbor"

{ "ietf-dots-signal-channel:signal-config": { "mitigating-config": { "heartbeat-interval": { "current-value": 30 }, "missing-hb-allowed": { "current-value": 15 }, "probing-rate": { "current-value": 15 }, "max-retransmit": { "current-value": 3 }, "ack-timeout": { "current-value-decimal": "2.00" }, "ack-random-factor": { "current-value-decimal": "1.50" } }, "idle-config": { "heartbeat-interval": { "current-value": 0 }, "max-retransmit": { "current-value": 3 }, "ack-timeout": { "current-value-decimal": "2.00" }, "ack-random-factor": { "current-value-decimal": "1.50" } } } }

Figure 23: PUT to Convey the Configuration Parameters



The DOTS server indicates the result of processing the PUT request using CoAP response codes:

o If the request is missing a mandatory attribute, does not include a ’sid’ Uri-Path, or contains one or more invalid or unknown parameters, 4.00 (Bad Request) MUST be returned in the response.

o If the DOTS server does not find the ’sid’ parameter value conveyed in the PUT request in its configuration data and if the DOTS server has accepted the configuration parameters, then a response code 2.01 (Created) MUST be returned in the response.

o If the DOTS server finds the ’sid’ parameter value conveyed in the PUT request in its configuration data and if the DOTS server has accepted the updated configuration parameters, 2.04 (Changed) MUST be returned in the response.

o If any of the ’heartbeat-interval’, ’missing-hb-allowed’, ’probing-rate’, ’max-retransmit’, ’target-protocol’, ’ack- timeout’, and ’ack-random-factor’ attribute values are not acceptable to the DOTS server, 4.22 (Unprocessable Entity) MUST be returned in the response. Upon receipt of this error code, the DOTS client SHOULD retrieve the maximum and minimum attribute values acceptable to the DOTS server (Section 4.5.1).

The DOTS client may re-try and send the PUT request with updated attribute values acceptable to the DOTS server.

A DOTS client may issue a GET message with ’sid’ Uri-Path parameter to retrieve the negotiated configuration. The response does not need to include ’sid’ in its message body.

4.5.3. Configuration Freshness and Notifications

Max-Age Option (Section 5.10.5 of [RFC7252]) SHOULD be returned by a DOTS server to associate a validity time with a configuration it sends. This feature allows the update of the configuration data if a change occurs at the DOTS server side. For example, the new configuration may instruct a DOTS client to cease heartbeats or reduce heartbeat frequency.

It is NOT RECOMMENDED to return a Max-Age Option set to 0.

Returning a Max-Age Option set to 2**32-1 is equivalent to associating an infinite lifetime with the configuration.

If a non-zero value of Max-Age Option is received by a DOTS client, it MUST issue a GET request with ’sid’ Uri-Path parameter to retrieve



the current and acceptable configuration before the expiry of the value enclosed in the Max-Age option. This request is considered by the client and the server as a means to refresh the configuration parameters for the signal channel. When a DDoS attack is active, refresh requests MUST NOT be sent by DOTS clients and the DOTS server MUST NOT terminate the (D)TLS session after the expiry of the value returned in Max-Age Option.

If Max-Age Option is not returned in a response, the DOTS client initiates GET requests to refresh the configuration parameters each 60 seconds (Section 5.10.5 of [RFC7252]). To prevent such overload, it is RECOMMENDED that DOTS servers return a Max-Age Option in GET responses. Considerations related to which value to use and how such value is set, are implementation- and deployment-specific.

If an Observe Option set to 0 is included in the configuration request, the DOTS server sends notifications of any configuration change (Section 4.2 of [RFC7641]).

If a DOTS server detects that a misbehaving DOTS client does not contact the DOTS server after the expiry of Max-Age and retrieve the signal channel configuration data, it MAY terminate the (D)TLS session. A (D)TLS session is terminated by the receipt of an authenticated message that closes the connection (e.g., a fatal alert (Section 6 of [RFC8446])).

4.5.4. Delete DOTS Signal Channel Session Configuration

A DELETE request is used to delete the installed DOTS signal channel session configuration data (Figure 24).

Header: DELETE (Code=0.04) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "config" Uri-Path: "sid=123"

Figure 24: Delete Configuration

The DOTS server resets the DOTS signal channel session configuration back to the default values and acknowledges a DOTS client’s request to remove the DOTS signal channel session configuration using 2.02 (Deleted) response code.

Upon bootstrapping or reboot, a DOTS client MAY send a DELETE request to set the configuration parameters to default values. Such a request does not include any ’sid’.



4.6. Redirected Signaling

Redirected DOTS signaling is discussed in detail in Section 3.2.2 of [I-D.ietf-dots-architecture].

If a DOTS server wants to redirect a DOTS client to an alternative DOTS server for a signal session, then the response code 5.03 (Service Unavailable) will be returned in the response to the DOTS client.

The DOTS server can return the error response code 5.03 in response to a request from the DOTS client or convey the error response code 5.03 in a unidirectional notification response from the DOTS server.

The DOTS server in the error response conveys the alternate DOTS server’s FQDN, and the alternate DOTS server’s IP address(es) values in the CBOR body (Figure 25).

{ "ietf-dots-signal-channel:redirected-signal": { "alt-server": "string", "alt-server-record": [ "string" ] }

Figure 25: Redirected Server Error Response Body Schema


alt-server: FQDN of an alternate DOTS server.


alt-server-record: A list of IP addresses of an alternate DOTS server.


The DOTS server returns the Time to live (TTL) of the alternate DOTS server in a Max-Age Option. That is, the time interval that the alternate DOTS server may be cached for use by a DOTS client. A Max- Age Option set to 2**32-1 is equivalent to receiving an infinite TTL. This value means that the alternate DOTS server is to be used until the alternate DOTS server redirects the traffic with another 5.03 response which encloses an alternate server.



A Max-Age Option set to ’0’ may be returned for redirecting mitigation requests. Such value means that the redirection applies only for the mitigation request in progress. Returning short TTL in a Max-Age Option may adversely impact DOTS clients on slow links. Returning short values should be avoided under such conditions.

If the alternate DOTS server TTL has expired, the DOTS client MUST use the DOTS server(s), that was provisioned using means discussed in Section 4.1. This fall back mechanism is triggered immediately upon expiry of the TTL, except when a DDoS attack is active.

Requests issued by misbehaving DOTS clients which do not honor the TTL conveyed in the Max-Age Option or react to explicit re-direct messages can be rejected by DOTS servers.

Figure 26 shows a 5.03 response example to convey the DOTS alternate server ’alt-server.example’ together with its IP addresses 2001:db8:6401::1 and 2001:db8:6401::2.

{ "ietf-dots-signal-channel:redirected-signal": { "alt-server": "alt-server.example", "alt-server-record": [ "2001:db8:6401::1", "2001:db8:6401::2" ] }

Figure 26: Example of Redirected Server Error Response Body

When the DOTS client receives 5.03 response with an alternate server included, it considers the current request as failed, but SHOULD try re-sending the request to the alternate DOTS server. During a DDoS attack, the DNS server may be the target of another DDoS attack, alternate DOTS server’s IP addresses conveyed in the 5.03 response help the DOTS client skip DNS lookup of the alternate DOTS server, at the cost of trusting the first DOTS server to provide accurate information. The DOTS client can then try to establish a UDP or a TCP session with the alternate DOTS server. The DOTS client MAY implement a method to construct IPv4-embedded IPv6 addresses [RFC6052]; this is required to handle the scenario where an IPv6-only DOTS client communicates with an IPv4-only alternate DOTS server.

If the DOTS client has been redirected to a DOTS server to which it has already communicated with within the last five (5) minutes, it MUST ignore the redirection and try to contact other DOTS servers listed in the local configuration or discovered using dynamic means such as DHCP or SRV procedures [I-D.ietf-dots-server-discovery]. It



is RECOMMENDED that DOTS clients support means to alert administrators about redirect loops.

4.7. Heartbeat Mechanism

To provide an indication of signal health and distinguish an ’idle’ signal channel from a ’disconnected’ or ’defunct’ session, the DOTS agent sends a heartbeat over the signal channel to maintain its half of the channel (also, aligned with the "consents" recommendation in Section 6 of [RFC8085]). The DOTS agent similarly expects a heartbeat from its peer DOTS agent, and may consider a session terminated in the prolonged absence of a peer agent heartbeat. Concretely, while the communication between the DOTS agents is otherwise quiescent, the DOTS client will probe the DOTS server to ensure it has maintained cryptographic state and vice versa. Such probes can also keep firewalls and/or stateful translators bindings alive. This probing reduces the frequency of establishing a new handshake when a DOTS signal needs to be conveyed to the DOTS server.

Implementation Note: Given that CoAP roles can be multiplexed over the same session as discussed in [RFC7252] and already supported by CoAP implementations, both the DOTS client and server can send DOTS heartbeat requests.

The DOTS Heartbeat mechanism uses non-confirmable PUT requests (Figure 27) with an expected 2.04 (Changed) Response Code (Figure 28). This procedure occurs between a DOTS agent and its immediate peer DOTS agent. As such, this PUT request MUST NOT be relayed by a DOTS gateway. The PUT request used for DOTS heartbeat MUST NOT have a ’cuid’, ’cdid,’ or ’mid’ Uri-Path.

Header: PUT (Code=0.03) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "hb" Content-Format: "application/dots+cbor"

{ "ietf-dots-signal-channel:heartbeat": { "peer-hb-status": true } }

Figure 27: PUT to Check Peer DOTS Agent is Responding

The mandatory ’peer-hb-status’ attribute is set to ’true’ (or ’false’) to indicates that a DOTS agent is (or not) receiving heartbeat messages from its peer in the last (2 * heartbeat-interval)



period. Such information can be used by a peer DOTS agent to detect or confirm connectivity issues and react accordingly. For example, if a DOTS client receives 2.04 response for its heartbeat messages but no server-initiated heartbeat messages, the DOTS client sets ’peer-hb-status’ to ’false’. The DOTS server will need then to try another strategy for sending the heartbeats (e.g., adjust the heartbeat interval or send a server-initiated heartbeat immediately after receiving a client-initiated heartbeat message).

Header: (Code=2.04)

Figure 28: Response to a DOTS Heartbeat Request

DOTS servers MAY trigger their heartbeat requests immediately after receiving heartbeat probes from peer DOTS clients. As a reminder, it is the responsibility of DOTS clients to ensure that on-path translators/firewalls are maintaining a binding so that the same external IP address and/or port number is retained for the DOTS signal channel session.

Under normal traffic conditions (i.e., no attack is ongoing), if a DOTS agent does not receive any response from the peer DOTS agent for ’missing-hb-allowed’ number of consecutive heartbeat messages, it concludes that the DOTS signal channel session is disconnected. The DOTS client MUST then try to re-establish the DOTS signal channel session, preferably by resuming the (D)TLS session.

Note: If a new DOTS signal channel session cannot be established, the DOTS client SHOULD NOT retry to establish the DOTS signal channel session more frequently than every 300 seconds (5 minutes) and MUST NOT retry more frequently than every 60 seconds (1 minute). It is recommended that DOTS clients support means to alert administrators about the failure to establish a (D)TLS session.

In case of a massive DDoS attack that saturates the incoming link(s) to the DOTS client, all traffic from the DOTS server to the DOTS client will likely be dropped, although the DOTS server receives heartbeat requests in addition to DOTS messages sent by the DOTS client. In this scenario, DOTS clients MUST behave differently to handle message transmission and DOTS signal channel session liveliness during link saturation:

The DOTS client MUST NOT consider the DOTS signal channel session terminated even after a maximum ’missing-hb-allowed’ threshold is reached. The DOTS client SHOULD keep on using the current DOTS signal channel session to send heartbeat requests over it, so that



the DOTS server knows the DOTS client has not disconnected the DOTS signal channel session.

After the maximum ’missing-hb-allowed’ threshold is reached, the DOTS client SHOULD try to establish a new DOTS signal channel session. The DOTS client SHOULD send mitigation requests over the current DOTS signal channel session and, in parallel, send the mitigation requests over the new DOTS signal channel session. This may be handled, for example, by resumption of the (D)TLS session or using 0-RTT mode in DTLS 1.3 to piggyback the mitigation request in the ClientHello message.

As soon as the link is no longer saturated, if traffic from the DOTS server reaches the DOTS client over the current DOTS signal channel session, the DOTS client can stop the new DOTS signal channel session attempt or if a new DOTS signal channel session is successful then disconnect the current DOTS signal channel session.

If the DOTS server receives traffic from the peer DOTS client (e.g., peer DOTS client initiated heartbeats) but maximum ’missing-hb- allowed’ threshold is reached, the DOTS server MUST NOT consider the DOTS signal channel session disconnected. The DOTS server MUST keep on using the current DOTS signal channel session so that the DOTS client can send mitigation requests over the current DOTS signal channel session. In this case, the DOTS server can identify the DOTS client is under attack and the inbound link to the DOTS client (domain) is saturated. Furthermore, if the DOTS server does not receive a mitigation request from the DOTS client, it implies the DOTS client has not detected the attack or, if an attack mitigation is in progress, it implies the applied DDoS mitigation actions are not yet effective to handle the DDoS attack volume.

If the DOTS server does not receive any traffic from the peer DOTS client during the time span required to exhaust the maximum ’missing- hb-allowed’ threshold, the DOTS server concludes the session is disconnected. The DOTS server can then trigger pre-configured mitigation requests for this DOTS client (if any).

In DOTS over TCP, the sender of a DOTS heartbeat message has to allow up to ’heartbeat-interval’ seconds when waiting for a heartbeat reply. When a failure is detected by a DOTS client, it proceeds with the session recovery following the same approach as the one used for unreliable transports.



5. DOTS Signal Channel YANG Modules

This document defines a YANG [RFC7950] module for DOTS mitigation scope, DOTS signal channel session configuration data, DOTS redirection signaling, and DOTS heartbeats.

This YANG module (ietf-dots-signal-channel) defines the DOTS client interaction with the DOTS server as seen by the DOTS client. A DOTS server is allowed to update the non-configurable ’ro’ entities in the responses. This YANG module is not intended to be used via NETCONF/ RESTCONF for DOTS server management purposes; such module is out of the scope of this document. It serves only to provide a data model and encoding, but not a management data model.

A companion YANG module is defined to include a collection of types defined by IANA: "iana-dots-signal-channel" (Section 5.2).

5.1. Tree Structure

This document defines the YANG module "ietf-dots-signal-channel" (Section 5.3), which has the following tree structure. A DOTS signal message can be a mitigation, a configuration, a redirect, or a heartbeat message.

module: ietf-dots-signal-channel +--rw dots-signal +--rw (message-type)? +--:(mitigation-scope) | +--rw scope* [cuid mid] | +--rw cdid? string | +--rw cuid string | +--rw mid uint32 | +--rw target-prefix* inet:ip-prefix | +--rw target-port-range* [lower-port] | | +--rw lower-port inet:port-number | | +--rw upper-port? inet:port-number | +--rw target-protocol* uint8 | +--rw target-fqdn* inet:domain-name | +--rw target-uri* inet:uri | +--rw alias-name* string | +--rw lifetime? int32 | +--rw trigger-mitigation? boolean | +--ro mitigation-start? uint64 | +--ro status? iana-signal:status | +--ro conflict-information | | +--ro conflict-status? iana-signal:conflict-status | | +--ro conflict-cause? iana-signal:conflict-cause | | +--ro retry-timer? uint32



| | +--rw current-value-decimal? decimal64 | +--rw idle-config | +--rw heartbeat-interval | | +--ro max-value? uint16 | | +--ro min-value? uint16 | | +--rw current-value? uint16 | +--rw missing-hb-allowed | | +--ro max-value? uint16 | | +--ro min-value? uint16 | | +--rw current-value? uint16 | +--rw probing-rate | | +--ro max-value? uint16 | | +--ro min-value? uint16 | | +--rw current-value? uint16 | +--rw max-retransmit | | +--ro max-value? uint16 | | +--ro min-value? uint16 | | +--rw current-value? uint16 | +--rw ack-timeout | | +--ro max-value-decimal? decimal64 | | +--ro min-value-decimal? decimal64 | | +--rw current-value-decimal? decimal64 | +--rw ack-random-factor | +--ro max-value-decimal? decimal64 | +--ro min-value-decimal? decimal64 | +--rw current-value-decimal? decimal64 +--:(redirected-signal) | +--ro alt-server string | +--ro alt-server-record* inet:ip-address +--:(heartbeat) +--rw peer-hb-status boolean

5.2. IANA DOTS Signal Channel YANG Module

<CODE BEGINS> file "[email protected]" module iana-dots-signal-channel { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:iana-dots-signal-channel"; prefix iana-signal;

organization "IANA"; contact "Internet Assigned Numbers Authority

Postal: ICANN 12025 Waterfront Drive, Suite 300 Los Angeles, CA 90094-2536



United States of America Tel: +1 310 301 5800 <mailto:[email protected]>"; description "This module contains a collection of YANG data types defined by IANA and used for DOTS signal channel protocol.

Copyright (c) 2019 IETF Trust and the persons identified as authors of the code. All rights reserved.



revision 2019-01-17 { description "Initial revision."; reference "RFC XXXX: Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification"; }

typedef status { type enumeration { enum attack-mitigation-in-progress { value 1; description "Attack mitigation setup is in progress (e.g., changing the network path to re-route the inbound traffic to DOTS mitigator)."; } enum attack-successfully-mitigated { value 2; description "Attack is being successfully mitigated (e.g., traffic is redirected to a DDoS mitigator and attack traffic is dropped or blackholed)."; } enum attack-stopped { value 3; description "Attack has stopped and the DOTS client can



withdraw the mitigation request."; } enum attack-exceeded-capability { value 4; description "Attack has exceeded the mitigation provider capability."; } enum dots-client-withdrawn-mitigation { value 5; description "DOTS client has withdrawn the mitigation request and the mitigation is active but terminating."; } enum attack-mitigation-terminated { value 6; description "Attack mitigation is now terminated."; } enum attack-mitigation-withdrawn { value 7; description "Attack mitigation is withdrawn."; } enum attack-mitigation-signal-loss { value 8; description "Attack mitigation will be triggered for the mitigation request only when the DOTS signal channel session is lost."; } } description "Enumeration for status reported by the DOTS server."; }

typedef conflict-status { type enumeration { enum request-inactive-other-active { value 1; description "DOTS Server has detected conflicting mitigation requests from different DOTS clients. This mitigation request is currently inactive until the conflicts are resolved. Another mitigation request is active."; }



enum request-active { value 2; description "DOTS Server has detected conflicting mitigation requests from different DOTS clients. This mitigation request is currently active."; } enum all-requests-inactive { value 3; description "DOTS Server has detected conflicting mitigation requests from different DOTS clients. All conflicting mitigation requests are inactive."; } } description "Enumeration for conflict status."; }

typedef conflict-cause { type enumeration { enum overlapping-targets { value 1; description "Overlapping targets. conflict-scope provides more details about the exact conflict."; } enum conflict-with-acceptlist { value 2; description "Conflicts with an existing accept-list.

This code is returned when the DDoS mitigation detects that some of the source addresses/prefixes listed in the accept-list ACLs are actually attacking the target."; } enum cuid-collision { value 3; description "Conflicts with the cuid used by another DOTS client."; } } description "Enumeration for conflict causes."; }



typedef attack-status { type enumeration { enum under-attack { value 1; description "The DOTS client determines that it is still under attack."; } enum attack-successfully-mitigated { value 2; description "The DOTS client determines that the attack is successfully mitigated."; } } description "Enumeration for attack status codes."; } } <CODE ENDS>

5.3. IETF DOTS Signal Channel YANG Module

This module uses the common YANG types defined in [RFC6991] and types defined in [I-D.ietf-dots-data-channel].

<CODE BEGINS> file "[email protected]" module ietf-dots-signal-channel { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-dots-signal-channel"; prefix signal;

import ietf-inet-types { prefix inet; reference "Section 4 of RFC 6991"; } import ietf-yang-types { prefix yang; reference "Section 3 of RFC 6991"; } import ietf-dots-data-channel { prefix ietf-data; reference "RFC YYYY: Distributed Denial-of-Service Open Threat Signaling (DOTS) Data Channel Specification"; } import iana-dots-signal-channel { prefix iana-signal;



}

organization "IETF DDoS Open Threat Signaling (DOTS) Working Group"; contact "WG Web: <https://datatracker.ietf.org/wg/dots/> WG List: <mailto:[email protected]>

Editor: Konda, Tirumaleswar Reddy <mailto:[email protected]>

Editor: Mohamed Boucadair <mailto:[email protected]>

Author: Prashanth Patil <mailto:[email protected]>

Author: Andrew Mortensen <mailto:[email protected]>

Author: Nik Teague <mailto:[email protected]>"; description "This module contains YANG definition for the signaling messages exchanged between a DOTS client and a DOTS server.

Copyright (c) 2019 IETF Trust and the persons identified as authors of the code. All rights reserved.



revision 2019-11-13 { description "Initial revision."; reference "RFC XXXX: Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification"; }

/*



* Groupings */

grouping mitigation-scope { description "Specifies the scope of the mitigation request."; list scope { key "cuid mid"; description "The scope of the request."; leaf cdid { type string; description "The cdid should be included by a server-domain DOTS gateway to propagate the client domain identification information from the gateway’s client-facing-side to the gateway’s server-facing-side, and from the gateway’s server-facing-side to the DOTS server.

It may be used by the final DOTS server for policy enforcement purposes."; } leaf cuid { type string; description "A unique identifier that is generated by a DOTS client to prevent request collisions. It is expected that the cuid will remain consistent throughout the lifetime of the DOTS client."; } leaf mid { type uint32; description "Mitigation request identifier.

This identifier must be unique for each mitigation request bound to the DOTS client."; } uses ietf-data:target; leaf-list alias-name { type string; description "An alias name that points to a resource."; } leaf lifetime { type int32;



units "seconds"; default "3600"; description "Indicates the lifetime of the mitigation request.

A lifetime of ’0’ in a mitigation request is an invalid value.

A lifetime of negative one (-1) indicates indefinite lifetime for the mitigation request."; } leaf trigger-mitigation { type boolean; default "true"; description "If set to ’false’, DDoS mitigation will not be triggered unless the DOTS signal channel session is lost."; } leaf mitigation-start { type uint64; config false; description "Mitigation start time is represented in seconds relative to 1970-01-01T00:00:00Z in UTC time."; } leaf status { type iana-signal:status; config false; description "Indicates the status of a mitigation request. It must be included in responses only."; } container conflict-information { config false; description "Indicates that a conflict is detected. Must only be used for responses."; leaf conflict-status { type iana-signal:conflict-status; description "Indicates the conflict status."; } leaf conflict-cause { type iana-signal:conflict-cause; description "Indicates the cause of the conflict."; }



leaf retry-timer { type uint32; units "seconds"; description "The DOTS client must not re-send the same request that has a conflict before the expiry of this timer."; } container conflict-scope { description "Provides more information about the conflict scope."; uses ietf-data:target { when "../conflict-cause = ’overlapping-targets’"; } leaf-list alias-name { when "../../conflict-cause = ’overlapping-targets’"; type string; description "Conflicting alias-name."; } list acl-list { when "../../conflict-cause = ’conflict-with-acceptlist’"; key "acl-name"; description "List of conflicting ACLs as defined in the DOTS data channel. These ACLs are uniquely defined by cuid and acl-name."; leaf acl-name { type leafref { path "/ietf-data:dots-data/ietf-data:dots-client/" + "ietf-data:acls/ietf-data:acl/ietf-data:name"; } description "Reference to the conflicting ACL name bound to a DOTS client."; } leaf acl-type { type leafref { path "/ietf-data:dots-data/ietf-data:dots-client/" + "ietf-data:acls/ietf-data:acl/ietf-data:type"; } description "Reference to the conflicting ACL type bound to a DOTS client."; } } leaf mid { when "../../conflict-cause = ’overlapping-targets’";



type leafref { path "../../../mid"; } description "Reference to the conflicting ’mid’ bound to the same DOTS client."; } } } leaf bytes-dropped { type yang:zero-based-counter64; units "bytes"; config false; description "The total dropped byte count for the mitigation request since the attack mitigation is triggered. The count wraps around when it reaches the maximum value of counter64 for dropped bytes."; } leaf bps-dropped { type yang:gauge64; config false; description "The average number of dropped bits per second for the mitigation request since the attack mitigation is triggered. This should be over five-minute intervals (that is, measuring bytes into five-minute buckets and then averaging these buckets over the time since the mitigation was triggered)."; } leaf pkts-dropped { type yang:zero-based-counter64; config false; description "The total number of dropped packet count for the mitigation request since the attack mitigation is triggered. The count wraps around when it reaches the maximum value of counter64 for dropped packets."; } leaf pps-dropped { type yang:gauge64; config false; description "The average number of dropped packets per second for the mitigation request since the attack mitigation is triggered. This should be over five-minute intervals (that is, measuring packets



into five-minute buckets and then averaging these buckets over the time since the mitigation was triggered)."; } leaf attack-status { type iana-signal:attack-status; description "Indicates the status of an attack as seen by the DOTS client."; } } }

grouping config-parameters { description "Subset of DOTS signal channel session configuration."; container heartbeat-interval { description "DOTS agents regularly send heartbeats to each other after mutual authentication is successfully completed in order to keep the DOTS signal channel open."; leaf max-value { type uint16; units "seconds"; config false; description "Maximum acceptable heartbeat-interval value."; } leaf min-value { type uint16; units "seconds"; config false; description "Minimum acceptable heartbeat-interval value."; } leaf current-value { type uint16; units "seconds"; default "30"; description "Current heartbeat-interval value.

’0’ means that heartbeat mechanism is deactivated."; } } container missing-hb-allowed { description



"Maximum number of missing heartbeats allowed."; leaf max-value { type uint16; config false; description "Maximum acceptable missing-hb-allowed value."; } leaf min-value { type uint16; config false; description "Minimum acceptable missing-hb-allowed value."; } leaf current-value { type uint16; default "15"; description "Current missing-hb-allowed value."; } } container probing-rate { description "The limit for sending non-confirmable messages with no response."; leaf max-value { type uint16; units "byte/second"; config false; description "Maximum acceptable probing-rate value."; } leaf min-value { type uint16; units "byte/second"; config false; description "Minimum acceptable probing-rate value."; } leaf current-value { type uint16; units "byte/second"; default "5"; description "Current probing-rate value."; } } container max-retransmit { description



"Maximum number of retransmissions of a Confirmable message."; leaf max-value { type uint16; config false; description "Maximum acceptable max-retransmit value."; } leaf min-value { type uint16; config false; description "Minimum acceptable max-retransmit value."; } leaf current-value { type uint16; default "3"; description "Current max-retransmit value."; } } container ack-timeout { description "Initial retransmission timeout value."; leaf max-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; config false; description "Maximum ack-timeout value."; } leaf min-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; config false; description "Minimum ack-timeout value."; } leaf current-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; default "2";



description "Current ack-timeout value."; } } container ack-random-factor { description "Random factor used to influence the timing of retransmissions."; leaf max-value-decimal { type decimal64 { fraction-digits 2; } config false; description "Maximum acceptable ack-random-factor value."; } leaf min-value-decimal { type decimal64 { fraction-digits 2; } config false; description "Minimum acceptable ack-random-factor value."; } leaf current-value-decimal { type decimal64 { fraction-digits 2; } default "1.5"; description "Current ack-random-factor value."; } } }

grouping signal-config { description "DOTS signal channel session configuration."; leaf sid { type uint32; mandatory true; description "An identifier for the DOTS signal channel session configuration data."; } container mitigating-config { description "Configuration parameters to use when a mitigation



is active."; uses config-parameters; } container idle-config { description "Configuration parameters to use when no mitigation is active."; uses config-parameters; } }

grouping redirected-signal { description "Grouping for the redirected signaling."; leaf alt-server { type string; config false; mandatory true; description "FQDN of an alternate server."; } leaf-list alt-server-record { type inet:ip-address; config false; description "List of records for the alternate server."; } }

/* * Main Container for DOTS Signal Channel */

container dots-signal { description "Main container for DOTS signal message.

A DOTS signal message can be a mitigation, a configuration, or a redirected signal message."; choice message-type { description "Can be a mitigation, a configuration, or a redirect message."; case mitigation-scope { description "Mitigation scope of a mitigation message."; uses mitigation-scope; }



case signal-config { description "Configuration message."; uses signal-config; } case redirected-signal { description "Redirected signaling."; uses redirected-signal; } case heartbeat { description "DOTS heartbeats."; leaf peer-hb-status { type boolean; mandatory true; description "Indicates whether a DOTS agent receives heartbeats from its peer. The value is set to ’true’ if the DOTS agent is receiving heartbeat messages from its peer."; } } } } } <CODE ENDS>

6. YANG/JSON Mapping Parameters to CBOR

All parameters in the payload of the DOTS signal channel MUST be mapped to CBOR types as shown in Table 4 and are assigned an integer key to save space.

o Note: Implementers must check that the mapping output provided by their YANG-to-CBOR encoding schemes is aligned with the content of Table 4. For example, some CBOR and JSON types for enumerations and the 64-bit quantities can differ depending on the encoder used.

The CBOR key values are divided into two types: comprehension- required and comprehension-optional. DOTS agents can safely ignore comprehension-optional values they don’t understand, but cannot successfully process a request if it contains comprehension-required values that are not understood. The 4.00 response SHOULD include a diagnostic payload describing the unknown comprehension-required CBOR key values. The initial set of CBOR key values defined in this specification are of type comprehension-required.



(D)TLS RFCs for discussion of these security issues. DOTS agents MUST adhere to the (D)TLS implementation recommendations and security considerations of [RFC7525] except with respect to (D)TLS version. Since DOTS signal channel encryption relying upon (D)TLS is virtually a green-field deployment, DOTS agents MUST implement only (D)TLS 1.2 or later.

When a DOTS client is configured with a domain name of the DOTS server, and connects to its configured DOTS server, the server may present it with a PKIX certificate. In order to ensure proper authentication, a DOTS client MUST verify the entire certification path per [RFC5280]. Additionally, the DOTS client MUST use [RFC6125] validation techniques to compare the domain name with the certificate provided. Certification authorities that issue DOTS server certificates SHOULD support the DNS-ID and SRV-ID identifier types. DOTS server SHOULD prefer the use of DNS-ID and SRV-ID over CN-ID identifier types in certificate requests (as described in Section 2.3 of [RFC6125]) and the wildcard character ’*’ SHOULD NOT be included in the presented identifier. DOTS doesn’t use URI-IDs for server identity verification.

A key challenge to deploying DOTS is the provisioning of DOTS clients, including the distribution of keying material to DOTS clients to enable the required mutual authentication of DOTS agents. Enrollment over Secure Transport (EST) [RFC7030] defines a method of certificate enrollment by which domains operating DOTS servers may provide DOTS clients with all the necessary cryptographic keying material, including a private key and a certificate to authenticate themselves. One deployment option is DOTS clients behave as EST clients for certificate enrollment from an EST server provisioned by the mitigation provider. This document does not specify which EST or other mechanism the DOTS client uses to achieve initial enrollment.

The Server Name Indication (SNI) extension [RFC6066] defines a mechanism for a client to tell a (D)TLS server the name of the server it wants to contact. This is a useful extension for hosting environments where multiple virtual servers are reachable over a single IP address. The DOTS client may or may not know if it is interacting with a DOTS server in a virtual server hosting environment, so the DOTS client SHOULD include the DOTS server FQDN in the SNI extension.

Implementations compliant with this profile MUST implement all of the following items:

o DTLS record replay detection (Section 3.3 of [RFC6347]) or an equivalent mechanism to protect against replay attacks.



o DTLS session resumption without server-side state to resume session and convey the DOTS signal.

o At least one of raw public keys [RFC7250] or PSK handshake [RFC4279] with (EC)DHE key exchange which reduces the size of the ServerHello, and can be used by DOTS agents that cannot obtain certificates.

Implementations compliant with this profile SHOULD implement all of the following items to reduce the delay required to deliver a DOTS signal channel message:

o TLS False Start [RFC7918] which reduces round-trips by allowing the TLS client’s second flight of messages (ChangeCipherSpec) to also contain the DOTS signal. TLS False Start is formally defined for use with TLS, but the same technique is applicable to DTLS as well.

o Cached Information Extension [RFC7924] which avoids transmitting the server’s certificate and certificate chain if the client has cached that information from a previous TLS handshake.

Compared to UDP, DOTS signal channel over TCP requires an additional round-trip time (RTT) of latency to establish a TCP connection. DOTS implementations are encouraged to implement TCP Fast Open [RFC7413] to eliminate that RTT.

7.2. (D)TLS 1.3 Considerations

TLS 1.3 provides critical latency improvements for connection establishment over TLS 1.2. The DTLS 1.3 protocol [I-D.ietf-tls-dtls13] is based upon the TLS 1.3 protocol and provides equivalent security guarantees. (D)TLS 1.3 provides two basic handshake modes the DOTS signal channel can take advantage of:

o A full handshake mode in which a DOTS client can send a DOTS mitigation request message after one round trip and the DOTS server immediately responds with a DOTS mitigation response. This assumes no packet loss is experienced.

o 0-RTT mode in which the DOTS client can authenticate itself and send DOTS mitigation request messages in the first message, thus reducing handshake latency. 0-RTT only works if the DOTS client has previously communicated with that DOTS server, which is very likely with the DOTS signal channel.

The DOTS client has to establish a (D)TLS session with the DOTS server during ’idle’ time and share a PSK.



During a DDoS attack, the DOTS client can use the (D)TLS session to convey the DOTS mitigation request message and, if there is no response from the server after multiple retries, the DOTS client can resume the (D)TLS session in 0-RTT mode using PSK.

DOTS servers that support (D)TLS 1.3 MAY allow DOTS clients to send early data (0-RTT). DOTS clients MUST NOT send "CoAP Ping" as early data; such messages MUST be rejected by DOTS servers. Section 8 of [RFC8446] discusses some mechanisms to implement to limit the impact of replay attacks on 0-RTT data. If the DOTS server accepts 0-RTT, it MUST implement one of these mechanisms to prevent replay at the TLS layer. A DOTS server can reject 0-RTT by sending a TLS HelloRetryRequest.

The DOTS signal channel messages sent as early data by the DOTS client are idempotent requests. As a reminder, the Message ID (Section 3 of [RFC7252]) is changed each time a new CoAP request is sent, and the Token (Section 5.3.1 of [RFC7252]) is randomized in each CoAP request. The DOTS server(s) MUST use the Message ID and the Token in the DOTS signal channel message to detect replay of early data at the application layer, and accept 0-RTT data at most once from the same DOTS client. This anti-replay defense requires sharing the Message ID and the Token in the 0-RTT data between DOTS servers in the DOTS server domain. DOTS servers do not rely on transport coordinates to identify DOTS peers. As specified in Section 4.4.1, DOTS servers couple the DOTS signal channel sessions using the DOTS client identity and optionally the ’cdid’ parameter value. Furthermore, ’mid’ value is monotonically increased by the DOTS client for each mitigation request, attackers replaying mitigation requests with lower numeric ’mid’ values and overlapping scopes with mitigation requests having higher numeric ’mid’ values will be rejected systematically by the DOTS server. Likewise, ’sid’ value is monotonically increased by the DOTS client for each configuration request (Section 4.5.2), attackers replaying configuration requests with lower numeric ’sid’ values will be rejected by the DOTS server if it maintains a higher numeric ’sid’ value for this DOTS client.

Owing to the aforementioned protections, all DOTS signal channel requests are safe to transmit in TLS 1.3 as early data. Refer to [I-D.boucadair-dots-earlydata] for more details.

A simplified TLS 1.3 handshake with 0-RTT DOTS mitigation request message exchange is shown in Figure 29.



DOTS Client DOTS Server

ClientHello (0-RTT DOTS signal message) --------> ServerHello {EncryptedExtensions} {Finished} <-------- [DOTS signal message] (end_of_early_data) {Finished} --------> [DOTS signal message] <-------> [DOTS signal message]

Note that: () Indicates messages protected 0-RTT keys {} Indicates messages protected using handshake keys [] Indicates messages protected using 1-RTT keys

Figure 29: A Simplified TLS 1.3 Handshake with 0-RTT

7.3. DTLS MTU and Fragmentation

To avoid DOTS signal message fragmentation and the subsequent decreased probability of message delivery, DOTS agents MUST ensure that the DTLS record fit within a single datagram. As a reminder, DTLS handles fragmentation and reassembly only for handshake messages and not for the application data (Section 4.1.1 of [RFC6347]). If the PMTU cannot be discovered, DOTS agents MUST assume a PMTU of 1280 bytes, as IPv6 requires that every link in the Internet have an MTU of 1280 octets or greater as specified in [RFC8200]. If IPv4 support on legacy or otherwise unusual networks is a consideration and the PMTU is unknown, DOTS implementations MAY assume on a PMTU of 576 bytes for IPv4 datagrams, as every IPv4 host must be capable of receiving a packet whose length is equal to 576 bytes as discussed in [RFC0791] and [RFC1122].

The DOTS client must consider the amount of record expansion expected by the DTLS processing when calculating the size of CoAP message that fits within the path MTU. Path MTU MUST be greater than or equal to [CoAP message size + DTLS 1.2 overhead of 13 octets + authentication overhead of the negotiated DTLS cipher suite + block padding] (Section 4.1.1.1 of [RFC6347]). If the total request size exceeds the path MTU then the DOTS client MUST split the DOTS signal into separate messages; for example, the list of addresses in the ’target- prefix’ parameter could be split into multiple lists and each list conveyed in a new PUT request.



Implementation Note: DOTS choice of message size parameters works well with IPv6 and with most of today’s IPv4 paths. However, with IPv4, it is harder to safely make sure that there is no IP fragmentation. If the IPv4 path MTU is unknown, implementations may want to limit themselves to more conservative IPv4 datagram sizes such as 576 bytes, as per [RFC0791].

8. Mutual Authentication of DOTS Agents & Authorization of DOTS Clients

(D)TLS based upon client certificate can be used for mutual authentication between DOTS agents. If, for example, a DOTS gateway is involved, DOTS clients and DOTS gateways must perform mutual authentication; only authorized DOTS clients are allowed to send DOTS signals to a DOTS gateway. The DOTS gateway and the DOTS server must perform mutual authentication; a DOTS server only allows DOTS signal channel messages from an authorized DOTS gateway, thereby creating a two-link chain of transitive authentication between the DOTS client and the DOTS server.

The DOTS server should support certificate-based client authentication. The DOTS client should respond to the DOTS server’s TLS CertificateRequest message with the PKIX certificate held by the DOTS client. DOTS client certificate validation must be performed as per [RFC5280] and the DOTS client certificate must conform to the [RFC5280] certificate profile. If a DOTS client does not support TLS client certificate authentication, it must support pre-shared key based or raw public key based client authentication.



+---------------------------------------------+ | example.com domain +---------+ | | | AAA | | | +---------------+ | Server | | | | Application | +------+--+ | | | server +<---------------+ ^ | | | (DOTS client) | | | | | +---------------+ | | | | V V | example.net domain | +-----+----+--+ | +---------------+ | +--------------+ | | | | | | | Guest +<----x---->+ DOTS +<------>+ DOTS | | | (DOTS client)| | gateway | | | server | | +--------------+ | | | | | | +----+--------+ | +---------------+ | ^ | | | | | +----------------+ | | | | DDoS detector | | | | | (DOTS client) +<-------------+ | | +----------------+ | +---------------------------------------------+

Figure 30: Example of Authentication and Authorization of DOTS Agents

In the example depicted in Figure 30, the DOTS gateway and DOTS clients within the ’example.com’ domain mutually authenticate. After the DOTS gateway validates the identity of a DOTS client, it communicates with the AAA server in the ’example.com’ domain to determine if the DOTS client is authorized to request DDoS mitigation. If the DOTS client is not authorized, a 4.01 (Unauthorized) is returned in the response to the DOTS client. In this example, the DOTS gateway only allows the application server and DDoS attack detector to request DDoS mitigation, but does not permit the user of type ’guest’ to request DDoS mitigation.

Also, DOTS gateways and servers located in different domains must perform mutual authentication (e.g., using certificates). A DOTS server will only allow a DOTS gateway with a certificate for a particular domain to request mitigation for that domain. In reference to Figure 30, the DOTS server only allows the DOTS gateway to request mitigation for ’example.com’ domain and not for other domains.




9.1. DOTS Signal Channel UDP and TCP Port Number

IANA is requested to assign the port number TBD to the DOTS signal channel protocol for both UDP and TCP from the "Service Name and Transport Protocol Port Number Registry" available at https://www.iana.org/assignments/service-names-port-numbers/service- names-port-numbers.xhtml.

The assignment of port number 4646 is strongly suggested, as 4646 is the ASCII decimal value for ".." (DOTS).

9.2. Well-Known ’dots’ URI

This document requests IANA to register the ’dots’ well-known URI (Table 5) in the Well-Known URIs registry (https://www.iana.org/assignments/well-known-uris/well-known- uris.xhtml) as defined by [RFC8615]:

+----------+----------------+---------------------+-----------------+ | URI | Change | Specification | Related | | suffix | controller | document(s) | information | +----------+----------------+---------------------+-----------------+ | dots | IETF | [RFCXXXX] | None | +----------+----------------+---------------------+-----------------+

Table 5: ’dots’ well-known URI

9.3. Media Type Registration

This document requests IANA to register the "application/dots+cbor" media type in the "Media Types" registry [IANA.MediaTypes] in the manner described in [RFC6838], which can be used to indicate that the content is a DOTS signal channel object:

o Type name: application o Subtype name: dots+cbor o Required parameters: N/A o Optional parameters: N/A o Encoding considerations: binary o Security considerations: See the Security Considerations section of [RFCXXXX] o Interoperability considerations: N/A o Published specification: [RFCXXXX] o Applications that use this media type: DOTS agents sending DOTS messages over CoAP over (D)TLS. o Fragment identifier considerations: N/A



o Additional information:

Magic number(s): N/A File extension(s): N/A Macintosh file type code(s): N/A o Person & email address to contact for further information: IESG, [email protected] o Intended usage: COMMON o Restrictions on usage: none o Author: See Authors’ Addresses section. o Change controller: IESG o Provisional registration? No

9.4. CoAP Content-Formats Registration

This document requests IANA to register the CoAP Content-Format ID for the "application/dots+cbor" media type in the "CoAP Content- Formats" registry [IANA.CoAP.Content-Formats] (0-255 range):

o Media Type: application/dots+cbor o Encoding: - o Id: TBD1 o Reference: [RFCXXXX]

9.5. CBOR Tag Registration

This section defines the DOTS CBOR tag as another means for applications to declare that a CBOR data structure is a DOTS signal channel object. Its use is optional and is intended for use in cases in which this information would not otherwise be known. DOTS CBOR tag is not required for DOTS signal channel protocol version specified in this document. If present, the DOTS tag MUST prefix a DOTS signal channel object.

This document requests IANA to register the DOTS signal channel CBOR tag in the "CBOR Tags" registry [IANA.CBOR.Tags] using the 24-255 range:

o CBOR Tag: TBD2 (please assign the same value as the Content- Format) o Data Item: DDoS Open Threat Signaling (DOTS) signal channel object o Semantics: DDoS Open Threat Signaling (DOTS) signal channel object, as defined in [RFCXXXX] o Description of Semantics: [RFCXXXX]



9.6. DOTS Signal Channel Protocol Registry

The document requests IANA to create a new registry, entitled "DOTS Signal Channel Registry". The following sections define sub- registries.

9.6.1. DOTS Signal Channel CBOR Key Values Sub-Registry

The document requests IANA to create a new sub-registry, entitled "DOTS Signal Channel CBOR Key Values".

The structure of this sub-registry is provided in Section 9.6.1.1. Section 9.6.1.2 provides how the registry is initially populated with the values in Table 4.

9.6.1.1. Registration Template

Parameter name: Parameter name as used in the DOTS signal channel.

CBOR Key Value: Key value for the parameter. The key value MUST be an integer in the 1-65535 range. The key values of the comprehension-required range (0x0001 - 0x3FFF) and of the comprehension-optional range (0x8000 - 0xBFFF) are assigned by IETF Review (Section 4.8 of [RFC8126]). The key values of the comprehension-optional range (0x4000 - 0x7FFF) are assigned by Specification Required (Section 4.6 of [RFC8126]) and of the comprehension-optional range (0xC000 - 0xFFFF) are reserved for Private Use (Section 4.1 of [RFC8126]).

Registration requests for the 0x4000 - 0x7FFF range are evaluated after a three-week review period on the dots-signal-reg- [email protected] mailing list, on the advice of one or more Designated Experts. However, to allow for the allocation of values prior to publication, the Designated Experts may approve registration once they are satisfied that such a specification will be published. New registration requests should be sent in the form of an email to the review mailing list; the request should use an appropriate subject (e.g., "Request to register CBOR Key Value for DOTS: example"). IANA will only accept new registrations from the Designated Experts, and will check that review was requested on the mailing list in accordance with these procedures.

Within the review period, the Designated Experts will either approve or deny the registration request, communicating this decision to the review list and IANA. Denials should include an



+------+-------------------------------+----------------+-----------+ | Code | Label | Description | Reference | +------+-------------------------------+----------------+-----------+ | 1 | under-attack | The DOTS | [RFCXXXX] | | | | client | | | | | determines | | | | | that it is | | | | | still under | | | | | attack. | | | 2 | attack-successfully-mitigated | The DOTS | [RFCXXXX] | | | | client | | | | | determines | | | | | that the | | | | | attack is | | | | | successfully | | | | | mitigated. | | +------+-------------------------------+----------------+-----------+


9.7. DOTS Signal Channel YANG Modules

This document requests IANA to register the following URIs in the "ns" subregistry within the "IETF XML Registry" [RFC3688]:

URI: urn:ietf:params:xml:ns:yang:ietf-dots-signal-channel Registrant Contact: The IESG. XML: N/A; the requested URI is an XML namespace.

URI: urn:ietf:params:xml:ns:yang:iana-dots-signal-channel Registrant Contact: IANA. XML: N/A; the requested URI is an XML namespace.

This document requests IANA to register the following YANG modules in the "YANG Module Names" subregistry [RFC7950] within the "YANG Parameters" registry.

Name: ietf-dots-signal-channel Namespace: urn:ietf:params:xml:ns:yang:ietf-dots-signal-channel Maintained by IANA: N Prefix: signal Reference: RFC XXXX

Name: iana-dots-signal-channel Namespace: urn:ietf:params:xml:ns:yang:iana-dots-signal-channel Maintained by IANA: Y Prefix: iana-signal Reference: RFC XXXX



This document defines the initial version of the IANA-maintained iana-dots-signal-channel YANG module. IANA is requested to add this note:

Status, conflict status, conflict cause, and attack status values must not be directly added to the iana-dots-signal-channel YANG module. They must instead be respectively added to the "DOTS Status Codes", "DOTS Conflict Status Codes", "DOTS Conflict Cause Codes", and "DOTS Attack Status Codes" registries.

When a ’status’, ’conflict-status’, ’conflict-cause’, or ’attack- status’ value is respectively added to the "DOTS Status Codes", "DOTS Conflict Status Codes", "DOTS Conflict Cause Codes", or "DOTS Attack Status Codes" registry, a new "enum" statement must be added to the iana-dots-signal-channel YANG module. The following "enum" statement, and substatements thereof, should be defined:

"enum": Replicates the label from the registry.

"value": Contains the IANA-assigned value corresponding to the ’status’, ’conflict-status’, ’conflict-cause’, or ’attack-status’.

"description": Replicates the description from the registry.

"reference": Replicates the reference from the registry and adds the title of the document.

When the iana-dots-signal-channel YANG module is updated, a new "revision" statement must be added in front of the existing revision statements.

IANA is requested to add this note to "DOTS Status Codes", "DOTS Conflict Status Codes", "DOTS Conflict Cause Codes", and "DOTS Attack Status Codes" registries:

When this registry is modified, the YANG module iana-dots-signal- channel must be updated as defined in [RFCXXXX].


High-level DOTS security considerations are documented in [RFC8612] and [I-D.ietf-dots-architecture].

Authenticated encryption MUST be used for data confidentiality and message integrity. The interaction between the DOTS agents requires Datagram Transport Layer Security (DTLS) or Transport Layer Security (TLS) with a cipher suite offering confidentiality protection, and



the guidance given in [RFC7525] MUST be followed to avoid attacks on (D)TLS. The (D)TLS protocol profile used for the DOTS signal channel is specified in Section 7.

If TCP is used between DOTS agents, an attacker may be able to inject RST packets, bogus application segments, etc., regardless of whether TLS authentication is used. Because the application data is TLS protected, this will not result in the application receiving bogus data, but it will constitute a DoS on the connection. This attack can be countered by using TCP-AO [RFC5925]. Although not widely adopted, if TCP-AO is used, then any bogus packets injected by an attacker will be rejected by the TCP-AO integrity check and therefore will never reach the TLS layer.

An attack vector that can be achieved if the ’cuid’ is guessable is a misbehaving DOTS client from within the client’s domain which uses the ’cuid’ of another DOTS client of the domain to delete or alter active mitigations. For this attack vector to happen, the misbehaving client needs to pass the security validation checks by the DOTS server, and eventually the checks of a client-domain DOTS gateway.

A similar attack can be achieved by a compromised DOTS client which can sniff the TLS 1.2 handshake, use the client certificate to identify the ’cuid’ used by another DOTS client. This attack is not possible if algorithms such as version 4 Universally Unique IDentifiers (UUIDs) in Section 4.4 of [RFC4122] are used to generate the ’cuid’ because such UUIDs are not a deterministic function of the client certificate. Likewise, this attack is not possible with TLS 1.3 because most of the TLS handshake is encrypted and the client certificate is not visible to eavesdroppers.

A compromised DOTS client can collude with a DDoS attacker to send mitigation request for a target resource, gets the mitigation efficacy from the DOTS server, and conveys the mitigation efficacy to the DDoS attacker to possibly change the DDoS attack strategy. Obviously, signaling an attack by the compromised DOTS client to the DOTS server will trigger attack mitigation. This attack can be prevented by monitoring and auditing DOTS clients to detect misbehavior and to deter misuse, and by only authorizing the DOTS client to request mitigation for specific target resources (e.g., an application server is authorized to request mitigation for its IP addresses but a DDoS mitigator can request mitigation for any target resource in the network). Furthermore, DOTS clients are typically co-located on network security services (e.g., firewall) and a compromised security service potentially can do a lot more damage to the network.



Rate-limiting DOTS requests, including those with new ’cuid’ values, from the same DOTS client defends against DoS attacks that would result in varying the ’cuid’ to exhaust DOTS server resources. Rate- limit policies SHOULD be enforced on DOTS gateways (if deployed) and DOTS servers.

In order to prevent leaking internal information outside a client- domain, DOTS gateways located in the client-domain SHOULD NOT reveal the identification information that pertains to internal DOTS clients (e.g., source IP address, client’s hostname) unless explicitly configured to do so.

DOTS servers MUST verify that requesting DOTS clients are entitled to trigger actions on a given IP prefix. That is, only actions on IP resources that belong to the DOTS client’ domain MUST be authorized by a DOTS server. The exact mechanism for the DOTS servers to validate that the target prefixes are within the scope of the DOTS client domain is deployment-specific.

The presence of DOTS gateways may lead to infinite forwarding loops, which is undesirable. To prevent and detect such loops, this document uses the Hop-Limit Option.

When FQDNs are used as targets, the DOTS server MUST rely upon DNS privacy enabling protocols (e.g., DNS over TLS [RFC7858] or DoH [RFC8484]) to prevent eavesdroppers from possibly identifying the target resources protected by the DDoS mitigation service, and means to ensure the target FQDN resolution is authentic (e.g., DNSSEC [RFC4034]).

CoAP-specific security considerations are discussed in Section 11 of [RFC7252], while CBOR-related security considerations are discussed in Section 8 of [RFC7049].

11. Contributors


o Jon Shallow, NCC Group, Email: [email protected]

o Mike Geller, Cisco Systems, Inc. 3250 Florida 33309 USA, Email: [email protected]

o Robert Moskowitz, HTT Consulting Oak Park, MI 42837 United States, Email: [email protected]

o Dan Wing, Email: [email protected]




Thanks to Christian Jacquenet, Roland Dobbins, Roman Danyliw, Michael Richardson, Ehud Doron, Kaname Nishizuka, Dave Dolson, Liang Xia, Gilbert Clark, Xialiang Frank, Jim Schaad, Klaus Hartke, Nesredien Suleiman, Stephen Farrell, and Yoshifumi Nishida for the discussion and comments.

The authors would like to give special thanks to Kaname Nishizuka and Jon Shallow for their efforts in implementing the protocol and performing interop testing at IETF Hackathons.

Thanks to the core WG for the recommendations on Hop-Limit and redirect signaling.

Special thanks to Benjamin Kaduk for the detailed AD review.

Thanks to Alexey Melnikov, Adam Roach, Suresh Krishnan, Mirja Kuehlewind, and Alissa Cooper for the review.

Thanks to Carsten Bormann for his review of the DOTS heartbeat mechanism.

13. References


[I-D.ietf-core-hop-limit] Boucadair, M., Reddy.K, T., and J. Shallow, "Constrained Application Protocol (CoAP) Hop-Limit Option", draft-ietf- core-hop-limit-07 (work in progress), October 2019.

[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 10.17487/RFC0791, September 1981, <https://www.rfc-editor.org/info/rfc791>.

[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, DOI 10.17487/RFC1122, October 1989, <https://www.rfc-editor.org/info/rfc1122>.




[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, <https://www.rfc-editor.org/info/rfc3688>.

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, <https://www.rfc-editor.org/info/rfc3986>.

[RFC4279] Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key Ciphersuites for Transport Layer Security (TLS)", RFC 4279, DOI 10.17487/RFC4279, December 2005, <https://www.rfc-editor.org/info/rfc4279>.

[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 2006, <https://www.rfc-editor.org/info/rfc4632>.

[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, <https://www.rfc-editor.org/info/rfc4648>.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, <https://www.rfc-editor.org/info/rfc5246>.

[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, <https://www.rfc-editor.org/info/rfc5280>.

[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) Extensions: Extension Definitions", RFC 6066, DOI 10.17487/RFC6066, January 2011, <https://www.rfc-editor.org/info/rfc6066>.




[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012, <https://www.rfc-editor.org/info/rfc6347>.

[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, July 2013, <https://www.rfc-editor.org/info/rfc6991>.

[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October 2013, <https://www.rfc-editor.org/info/rfc7049>.

[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J., Weiler, S., and T. Kivinen, "Using Raw Public Keys in Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250, June 2014, <https://www.rfc-editor.org/info/rfc7250>.

[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, <https://www.rfc-editor.org/info/rfc7252>.

[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, "Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 2015, <https://www.rfc-editor.org/info/rfc7525>.

[RFC7641] Hartke, K., "Observing Resources in the Constrained Application Protocol (CoAP)", RFC 7641, DOI 10.17487/RFC7641, September 2015, <https://www.rfc-editor.org/info/rfc7641>.

[RFC7918] Langley, A., Modadugu, N., and B. Moeller, "Transport Layer Security (TLS) False Start", RFC 7918, DOI 10.17487/RFC7918, August 2016, <https://www.rfc-editor.org/info/rfc7918>.

[RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security (TLS) Cached Information Extension", RFC 7924, DOI 10.17487/RFC7924, July 2016, <https://www.rfc-editor.org/info/rfc7924>.

[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, <https://www.rfc-editor.org/info/rfc7950>.



[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in the Constrained Application Protocol (CoAP)", RFC 7959, DOI 10.17487/RFC7959, August 2016, <https://www.rfc-editor.org/info/rfc7959>.

[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, March 2017, <https://www.rfc-editor.org/info/rfc8085>.

[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/info/rfc8126>.


[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017, <https://www.rfc-editor.org/info/rfc8200>.

[RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: Better Connectivity Using Concurrency", RFC 8305, DOI 10.17487/RFC8305, December 2017, <https://www.rfc-editor.org/info/rfc8305>.

[RFC8323] Bormann, C., Lemay, S., Tschofenig, H., Hartke, K., Silverajan, B., and B. Raymor, Ed., "CoAP (Constrained Application Protocol) over TCP, TLS, and WebSockets", RFC 8323, DOI 10.17487/RFC8323, February 2018, <https://www.rfc-editor.org/info/rfc8323>.

[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, <https://www.rfc-editor.org/info/rfc8446>.

[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers (URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019, <https://www.rfc-editor.org/info/rfc8615>.


[I-D.boucadair-dots-earlydata] Boucadair, M. and R. K, "Using Early Data in DOTS", draft- boucadair-dots-earlydata-00 (work in progress), January 2019.



[I-D.ietf-core-comi] Veillette, M., Stok, P., Pelov, A., Bierman, A., and I. Petrov, "CoAP Management Interface", draft-ietf-core- comi-08 (work in progress), September 2019.

[I-D.ietf-core-yang-cbor] Veillette, M., Petrov, I., and A. Pelov, "CBOR Encoding of Data Modeled with YANG", draft-ietf-core-yang-cbor-11 (work in progress), September 2019.

[I-D.ietf-dots-architecture] Mortensen, A., Reddy.K, T., Andreasen, F., Teague, N., and R. Compton, "Distributed-Denial-of-Service Open Threat Signaling (DOTS) Architecture", draft-ietf-dots- architecture-14 (work in progress), May 2019.

[I-D.ietf-dots-data-channel] Boucadair, M. and T. Reddy.K, "Distributed Denial-of- Service Open Threat Signaling (DOTS) Data Channel Specification", draft-ietf-dots-data-channel-31 (work in progress), July 2019.

[I-D.ietf-dots-multihoming] Boucadair, M., Reddy.K, T., and W. Pan, "Multi-homing Deployment Considerations for Distributed-Denial-of- Service Open Threat Signaling (DOTS)", draft-ietf-dots- multihoming-02 (work in progress), July 2019.

[I-D.ietf-dots-server-discovery] Boucadair, M. and T. Reddy.K, "Distributed-Denial-of- Service Open Threat Signaling (DOTS) Agent Discovery", draft-ietf-dots-server-discovery-06 (work in progress), November 2019.

[I-D.ietf-dots-use-cases] Dobbins, R., Migault, D., Moskowitz, R., Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS Open Threat Signaling", draft-ietf-dots-use-cases-20 (work in progress), September 2019.

[I-D.ietf-tls-dtls13] Rescorla, E., Tschofenig, H., and N. Modadugu, "The Datagram Transport Layer Security (DTLS) Protocol Version 1.3", draft-ietf-tls-dtls13-34 (work in progress), November 2019.



[IANA.CBOR.Tags] IANA, "Concise Binary Object Representation (CBOR) Tags", <http://www.iana.org/assignments/cbor-tags/cbor- tags.xhtml>.

[IANA.CoAP.Content-Formats] IANA, "CoAP Content-Formats", <http://www.iana.org/assignments/core-parameters/core- parameters.xhtml#content-formats>.

[IANA.MediaTypes] IANA, "Media Types", <http://www.iana.org/assignments/media-types>.

[proto_numbers] "IANA, "Protocol Numbers"", 2011, <http://www.iana.org/assignments/protocol-numbers>.

[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network Address Translator (Traditional NAT)", RFC 3022, DOI 10.17487/RFC3022, January 2001, <https://www.rfc-editor.org/info/rfc3022>.

[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Resource Records for the DNS Security Extensions", RFC 4034, DOI 10.17487/RFC4034, March 2005, <https://www.rfc-editor.org/info/rfc4034>.

[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally Unique IDentifier (UUID) URN Namespace", RFC 4122, DOI 10.17487/RFC4122, July 2005, <https://www.rfc-editor.org/info/rfc4122>.

[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram Congestion Control Protocol (DCCP)", RFC 4340, DOI 10.17487/RFC4340, March 2006, <https://www.rfc-editor.org/info/rfc4340>.


[RFC4787] Audet, F., Ed. and C. Jennings, "Network Address Translation (NAT) Behavioral Requirements for Unicast UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January 2007, <https://www.rfc-editor.org/info/rfc4787>.



[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol", RFC 4960, DOI 10.17487/RFC4960, September 2007, <https://www.rfc-editor.org/info/rfc4960>.

[RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common Mitigations", RFC 4987, DOI 10.17487/RFC4987, August 2007, <https://www.rfc-editor.org/info/rfc4987>.

[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, "Session Traversal Utilities for NAT (STUN)", RFC 5389, DOI 10.17487/RFC5389, October 2008, <https://www.rfc-editor.org/info/rfc5389>.

[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP Authentication Option", RFC 5925, DOI 10.17487/RFC5925, June 2010, <https://www.rfc-editor.org/info/rfc5925>.

[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, DOI 10.17487/RFC6052, October 2010, <https://www.rfc-editor.org/info/rfc6052>.

[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful NAT64: Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, April 2011, <https://www.rfc-editor.org/info/rfc6146>.

[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF)", RFC 6234, DOI 10.17487/RFC6234, May 2011, <https://www.rfc-editor.org/info/rfc6234>.

[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix Translation", RFC 6296, DOI 10.17487/RFC6296, June 2011, <https://www.rfc-editor.org/info/rfc6296>.

[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown, "Default Address Selection for Internet Protocol Version 6 (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012, <https://www.rfc-editor.org/info/rfc6724>.

[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013, <https://www.rfc-editor.org/info/rfc6838>.



[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and P. Selkirk, "Port Control Protocol (PCP)", RFC 6887, DOI 10.17487/RFC6887, April 2013, <https://www.rfc-editor.org/info/rfc6887>.

[RFC6888] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa, A., and H. Ashida, "Common Requirements for Carrier-Grade NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888, April 2013, <https://www.rfc-editor.org/info/rfc6888>.

[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed., "Enrollment over Secure Transport", RFC 7030, DOI 10.17487/RFC7030, October 2013, <https://www.rfc-editor.org/info/rfc7030>.

[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, <https://www.rfc-editor.org/info/rfc7413>.

[RFC7452] Tschofenig, H., Arkko, J., Thaler, D., and D. McPherson, "Architectural Considerations in Smart Object Networking", RFC 7452, DOI 10.17487/RFC7452, March 2015, <https://www.rfc-editor.org/info/rfc7452>.

[RFC7589] Badra, M., Luchuk, A., and J. Schoenwaelder, "Using the NETCONF Protocol over Transport Layer Security (TLS) with Mutual X.509 Authentication", RFC 7589, DOI 10.17487/RFC7589, June 2015, <https://www.rfc-editor.org/info/rfc7589>.

[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., and P. Hoffman, "Specification for DNS over Transport Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 2016, <https://www.rfc-editor.org/info/rfc7858>.

[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG", RFC 7951, DOI 10.17487/RFC7951, August 2016, <https://www.rfc-editor.org/info/rfc7951>.

[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, <https://www.rfc-editor.org/info/rfc8340>.

[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, <https://www.rfc-editor.org/info/rfc8484>.



[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499, January 2019, <https://www.rfc-editor.org/info/rfc8499>.


Appendix A. CUID Generation

The document recommends the use of SPKI to generate the ’cuid’. This design choice is motivated by the following reasons:

o SPKI is globally unique.

o It is deterministic.

o It allows to avoid extra cycles that may be induced by ’cuid’ collision.

o DOTS clients do not need to store the ’cuid’ in a persistent storage.

o It allows to detect compromised DOTS clients that do not adhere to the ’cuid’ generation algorithm.




Mohamed Boucadair (editor) Orange Rennes 35000 France








Nik Teague Iron Mountain Data Centers United Kingdom



DOTS R. DobbinsInternet-Draft Arbor NetworksIntended status: Informational D. MigaultExpires: January 21, 2018 Ericsson S. Fouant

R. Moskowitz HTT Consulting N. Teague Verisign L. Xia Huawei K. Nishizuka NTT Communications July 20, 2017

Use cases for DDoS Open Threat Signaling draft-ietf-dots-use-cases-07

Abstract

The DDoS Open Threat Signaling (DOTS) effort is intended to provide a protocol that facilitates interoperability between multivendor solutions/services. This document presents use cases to evaluate the interactions expected between the DOTS components as well as DOTS messaging exchanges. The purpose of describing use cases is to identify the interacting DOTS components, how they collaborate and what are the types of information to be exchanged.

Status of This Memo





Dobbins, et al. Expires January 21, 2018 [Page 1]

Internet-Draft DOTS Use Cases July 2017

Copyright Notice



Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology and Acronyms . . . . . . . . . . . . . . . . . . 3 2.1. Requirements Terminology . . . . . . . . . . . . . . . . 4 3. Use Cases Scenarios . . . . . . . . . . . . . . . . . . . . . 4 3.1. Inter-domain Use Cases . . . . . . . . . . . . . . . . . 5 3.1.1. End-customer with a single upstream transit provider offering DDoS mitigation services . . . . . . . . . . 5 3.1.2. End-customer with multiple upstream transit providers offering DDoS mitigation services . . . . . . . . . . 6 3.1.3. End-customer with multiple upstream transit providers, but only a single upstream transit provider offering DDoS mitigation services . . . . . 7 3.1.4. End-customer with an overlay DDoS mitigation managed security service provider (MSSP) . . . . . . . . . . 7 3.1.5. End-customer operating an application or service with an integrated DOTS client . . . . . . . . . . . . . . 9 3.1.6. End-customer operating a CPE network infrastructure device with an integrated DOTS client . . . . . . . . 9 3.1.7. End-customer with an out-of-band smartphone application featuring DOTS client capabilities . . . 9 3.1.8. MSSP as an end-customer requesting overflow DDoS mitigation assistance from other MSSPs . . . . . . . 10 3.2. Intra-domain Use Cases . . . . . . . . . . . . . . . . . 11 3.2.1. Suppression of outbound DDoS traffic originating from a consumer broadband access network . . . . . . . . . 11 3.2.2. Homenet DDoS Detection Collaboration for ISP network management . . . . . . . . . . . . . . . . . . . . . 13 3.2.3. DDoS Orchestration . . . . . . . . . . . . . . . . . 16 4. Security Considerations . . . . . . . . . . . . . . . . . . . 18 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19



7. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 7.1. Normative References . . . . . . . . . . . . . . . . . . 19 7.2. Informative References . . . . . . . . . . . . . . . . . 19 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 19

1. Introduction

Currently, distributed denial-of-service (DDoS) attack mitigation solutions are largely based upon siloed, proprietary communications schemes which result in vendor lock-in. As a side-effect, this makes the configuration, provisioning, operation, and activation of these solutions a highly manual and often time-consuming process. Additionally, coordination of multiple DDoS mitigation solutions simultaneously engaged in defending the same organization (resources) against DDoS attacks is fraught with both technical and process- related hurdles. This greatly increase operational complexity and often results in suboptimal DDoS attack mitigation efficacy.

The DDoS Open Threat Signaling (DOTS) effort is intended to specify a protocol that facilitates interoperability between multivendor DDoS mitigation solutions and ensures more automation in term of mitigation requests and attack characterization patterns. As DDoS solutions are broadly heterogeneous among different vendors, the primary goal for DOTS is to provide a high level interaction with these DDoS solutions such as initiating or terminating DDoS mitigation assistance.

It should be noted that DOTS is not in and of itself intended to perform orchestration functions duplicative of the functionality being developed by the [I2NSF] WG; rather, DOTS is intended to allow devices, services, and applications to request DDoS attack mitigation assistance and receive mitigation status updates.

These use cases are expected to provide inputs for the design of the DOTS protocol(s).

2. Terminology and Acronyms

This document makes use of the terms defined in [I-D.ietf-dots-requirements].

In addition, this document introduces the following terms:



Inter-domain: a DOTS communications relationship between distinct organizations with separate spans of administrative control. Typical inter-domain DOTS communication relationships would be between a DDoS mitigation service provider and an end-customer who requires DDoS mitigation assistance; between multiple DDoS mitigation service providers coordinating mutual defense of a mutual end-customer; or between DDoS mitigation service providers which are requesting additional DDoS mitigation assistance in for attacks which exceed their inherent DDoS mitigation capacities and/or capabilities.

Intra- domain: a DOTS communications relationship between various (network) elements that are owned and operated by the same administrative entity. A typical intra-domain DOTS communications relationship would be between DOTS agents [I-D.ietf-dots- requirements] within the same organization.

2.1. Requirements Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

3. Use Cases Scenarios

This section provides a high-level description of scenarios addressed by DOTS. In both sub-sections, the scenarios are provided in order to illustrate the use of DOTS in typical DDoS attack scenarios. They are not definitive, and other use cases are expected to emerge with widespread DOTS deployment.

All scenarios present a coordination between the targeted organization, the DDoS attack telemetry and the mitigator. The coordination and communication between these entities depends, for example, on the characteristic or functionality of the entity itself, the reliability of the information provided by DDoS attack telemetry, and the business relationship between the DDoS target domain and the mitigator.

More explicitly, in some cases, the DDoS attack telemetry may simply activate a DDoS mitigation, whereas in other cases, it may collaborate by providing some information about an attack. In some cases, the DDoS mitigation may be orchestrated, which includes selecting a specific appliance as well as starting/ending a mitigation.



3.1. Inter-domain Use Cases

Inter-domain DOTS deployment scenarios span two or more distinct spans of administrative control. A typical inter-domain DOTS deployment may consist of an endpoint network such as an Internet- connected enterprise requesting DDoS mitigation assistance from one or more upstream transit providers offering DDoS mitigation services, or from a topologically-distant MSSP offering cloud-based overlay DDoS mitigation services. DOTS may also be used to facilitate coordination of DDoS mitigation activities between mitigation providers.

Coordination between organizations making use of DOTS in such scenarios is necessary. Along with DOTS-specific tasks such as DOTS peering and validating the exchange of DOTS messaging between the relevant organizations, externalities relating to routing advertisements, authoritative DNS records (for DNS-based diversion), network access policies for DOTS nodes, service-level agreements (SLAs), and DDoS mitigation provisioning are required.

3.1.1. End-customer with a single upstream transit provider offering DDoS mitigation services

In this scenario, an enterprise network with self-hosted Internet- facing properties such as Web servers, authoritative DNS servers, and VoIP PBXes has an intelligent DDoS mitigation system (IDMS) deployed to protect those servers and applications from DDoS attacks. In addition to their on-premise DDoS defense capability, they have contracted with their Internet transit provider for DDoS mitigation services which threaten to overwhelm their transit link bandwidth.

The IDMS is configured such that if the incoming Internet traffic volume exceeds 50% of the provisioned upstream Internet transit link capacity, the IDMS will request DDoS mitigation assistance from the upstream transit provider.

The requests to trigger, manage, and finalize a DDoS mitigation between the enterprise IDMS and the transit provider is performed using DOTS. The enterprise IDMS implements a DOTS client while the transit provider implements a DOTS server which is integrated with their DDoS mitigation orchestration system.

When the IDMS detects an inbound DDoS attack targeting the enterprise servers and applications, it immediately begins mitigating the attack.

During the course of the attack, the inbound traffic volume exceeds the 50% threshold; the IDMS DOTS client signals the DOTS server on



the upstream transit provider network to initiate DDoS mitigation. The DOTS server signals the DOTS client that it can service this request, and mitigation is initiated on the transit provider network.

Over the course of the attack, the DOTS server on the transit provider network periodically signals the DOTS client on the enterprise IDMS in order to provide mitigation status information, statistics related to DDoS attack traffic mitigation, and related information. Once the DDoS attack has ended, the DOTS server signals the enterprise IDMS DOTS client that the attack has subsided.

The enterprise IDMS then requests that DDoS mitigation services on the upstream transit provider network be terminated. The DOTS server on the transit provider network receives this request, communicates with the transit provider orchestration system controlling its DDoS mitigation system to terminate attack mitigation, and once the mitigation has ended, confirms the end of upstream DDoS mitigation service to the enterprise IDMS DOTS client.

Note that communications between the enterprise DOTS client and the upstream transit provider DOTS server may take place in-band within the main Internet transit link between the enterprise and the transit provider; out-of-band via a separate, dedicated wireline network link utilized solely for DOTS signaling; or out-of-band via some other form of network connectivity such as a third-party wireless 4G network link.

3.1.2. End-customer with multiple upstream transit providers offering DDoS mitigation services

This scenario shares many characteristics with the above, but with the key difference that the enterprise in question is multi-homed, i.e., has two or more upstream transit providers, and that they all provide DDoS mitigation services.

In most cases, the communications model for a multi-homed model would be the same as in the single-homed model, merely duplicated in parallel. However, if two or more of the upstream transit providers have entered into a mutual DDoS mitigation agreement and have established DOTS peering between the participants, DDoS mitigation status messages may exchanged between the DOTS servers of the participants in order to provide a more complete picture of the DDoS attack scope, and allow for either automated or operator-assisted programmatic cooperative DDoS mitigation activities on the part of the transit providers.



3.1.3. End-customer with multiple upstream transit providers, but only a single upstream transit provider offering DDoS mitigation services

This scenario is similar to the multi-homed scenario referenced above; however, only one of the upstream transit providers in question offers DDoS mitigation services. In this situation, the enterprise would cease advertising the relevant network prefixes via the transit providers which do not provide DDoS mitigation services - or, in the case where the enterprise does not control its own routing, request that the upstream transit providers which do not offer DDoS mitigation services stop advertising the relevant network prefixes on their behalf.

Once it has been determined that the DDoS attack has ceased, the enterprise once again announces the relevant routes to the upstream transit providers which do not offer DDoS mitigation services, or requests that they resume announcing the relevant routes on behalf of the enterprise.

Note that falling back to a single transit provider has the effect of reducing available inbound transit bandwidth during a DDoS attack. Without proper planning and sufficient provisioning of both the link capacity and DDoS mitigation capacity of the sole transit provider offering DDoS mitigation services, this reduction of available bandwidth could lead to network link congestion caused by legitimate inbound network traffic. Therefore, careful planning and provisioning of both upstream transit bandwidth as well as DDoS mitigation capacity is required in scenarios of this nature.

The withdrawal and announcement of routing prefixes described in this use-case falls outside the scope of DOTS, although they could conceivably be triggered as a result of provider-specific orchestration triggered by the receipt of specific DOTS messages from the enterprise in question.

3.1.4. End-customer with an overlay DDoS mitigation managed security service provider (MSSP)

This use case details an enterprise that has a local DDoS detection and classification capability and may or may not have an on-premise mitigation capability. The enterprise is contracted with an overlay DDoS mitigation MSSP, topologically distant from the enterprise network (i.e., not a direct upstream transit provider), which can redirect (divert) traffic away from the enterprise, provide DDoS mitigation services services, and then forward (re-inject) legitimate traffic to the enterprise on an on-demand basis. In this scenario, diversion of Internet traffic destined for the enterprise network



into the overlay DDoS mitigation MSSP network is typically accomplished via eBGP announcements of the relevant enterprise network CIDR blocks, or via authoritative DNS subdomain-based mechanisms (other mechanisms are not precluded, these are merely the most common ones in use today).

The enterprise determines thresholds at which a request for mitigation is triggered indicating to the MSSP that inbound network traffic should be diverted into the MSSP network and that DDoS mitigation should be initiated. The enterprise may also elect to manually request diversion and mitigation via the MSSP network as desired.

The communications required to initiate, manage, and terminate active DDoS mitigation by the MSSP is performed using DOTS. The enterprise DDoS detection/classification system implements a DOTS client, while the MSSP implements a DOTS server integrated with its DDoS mitigation orchestration system. One or more out-of-band methods for initiating a mitigation request, such as a Web portal, a smartphone app, or voice support hotline, may also be made available by the MSSP.

When an attack is detected, an automated or manual DOTS mitigation request is be generated by the enterprise and sent to the MSSP. The enterprise DOTS mitigation request is processed by the MSSP DOTS server, which validates the origin of the request and passes it to the MSSP DDoS mitigation orchestration system, which then initiates active DDoS mitigation. This action will usually involve the diversion of all network traffic destined for the targeted enterprise into the MSSP DDoS mitigation network, where it will be subjected to further scrutiny, with DDoS attack traffic filtered by the MSSP. Successful mitigation of the DDoS attack will not only result preserving the availability of services and applications resident on the enterprise network, but will also prevent DDoS attack traffic from ingressing the networks of the enterprise upstream transit providers/peers.

The MSSP should signal via DOTS to the enterprise that a mitigation request has been received and acted upon, and should also include an update of the mitigation status. The MSSP may respond periodically with additional updates on the mitigation status to in order to enable the enterprise to make an informed decision on whether to maintain or terminate the mitigation. An alternative approach would be for the DOTS client mitigation request to include a time to live (TTL) for the mitigation, which may also be extended by the client should the attack still be ongoing as the TTL reaches expiration.

A variation of this use case may be that the enterprise is providing a DDoS monitoring and analysis service to customers whose networks



may be protected by any one of a number of third-party providers. The enterprise in question may integrate with these third-party providers using DOTS and signal accordingly when a customer is attacked - the MSSP may then manage the life-cycle of the attack mitigation on behalf of the enterprise.

3.1.5. End-customer operating an application or service with an integrated DOTS client

In this scenario, a Web server has a built-in mechanism to detect and classify DDoS attacks, which also incorporates a DOTS client. When an attack is detected, the self-defense mechanism is activated, and local DDoS mitigation is initiated.

The DOTS client built into the Web server has been configured to request DDoS mitigation services from an upstream transit provider or overlay MSSP once specific attack traffic thresholds have been reached, or certain network traffic conditions prevail. Once the specified conditions have been met, the DOTS communications dialogue and subsequent DDoS mitigation initiation and termination actions described above take place.

3.1.6. End-customer operating a CPE network infrastructure device with an integrated DOTS client

Similar to the above use-case featuring applications or services with built-in DDoS attack detection/classification and DOTS client capabilities, in this scenario, an end-customer network infrastructure CPE device such as a router, layer-3 switch, firewall, or load-balance incorporates both the functionality required to detect and classify incoming DDoS attacks as well as DOTS client functionality.

The subsequent DOTS communications dialogue and resultant DDoS mitigation initiation and termination activities take place in the same manner as the use-cases described above.

3.1.7. End-customer with an out-of-band smartphone application featuring DOTS client capabilities

This scenario would typically apply in a small office/home office (SOHO) setting, where the end-customer does not have CPE equipment or software capable of detecting/classifying/mitigating DDoS attack, yet still has a requirement for on-demand DDoS mitigation services. A smartphone application containing a DOTS client would be provided by the upstream transit mitigation provider or overlay DDoS MSSP to the SOHO end-customer; this application would allow a manual ’panic-



button’ to request the initiation and termination of DDoS mitigation services.

The DOTS communications dialogue and resultant DDoS mitigation initiation/status reporting/termination actions would then take place as in the other use-cases described above, with the end-customer DOTS client serving to display received status information while DDoS mitigation activities are taking place.

3.1.8. MSSP as an end-customer requesting overflow DDoS mitigation assistance from other MSSPs

This is a more complex use-case involving multiple DDoS MSSPs, whether transit operators, overlay MSSPs, or both. In this scenario, an MSSP has entered into a pre-arranged DDoS mitigation assistance agreement with one or more other DDoS MSSPs in order to ensure that sufficient DDoS mitigation capacity and/or capabilities may be activated in the event that a given DDoS attack threatens to overwhelm the ability of a given DDoS MSSP to mitigate the attack on its own.

BGP-based diversion (including relevant Letters of Authorization, or LoAs), DNS-based diversion (including relevant LoAs), traffic re- injection mechanisms such as Generic Routing Encapsulation (GRE) tunnels, provisioning of DDoS orchestration systems, et. al. must be arranged in advance between the DDoS MSSPs which are parties to the agreement. They should also be tested on a regular basis.

When a DDoS MSSP which is party to the agreement is nearing its capacity or ability to mitigate a given DDoS attack traffic, the DOTS client integrated with the MSSP DDoS mitigation orchestration system signals partner MSSPs to initiate network traffic diversion and DDoS mitigation activities. Ongoing attack and mitigation status messages may be passed between the DDoS MSSPs, and between the requesting MSSP and the ultimate end-customer of the attack.

The DOTS dialogues and resultant DDoS mitigation-related activities in this scenario progress as described in the other use-cases detailed above. Once the requesting DDoS MSSP is confident that the DDoS attack has either ceased or has fallen to levels of traffic/ complexity which they can handle on their own, the requesting DDoS MSSP DOTS client sends mitigation termination requests to the participating overflow DDoS MSSPs.



3.2. Intra-domain Use Cases

While many of the DOTS-specific elements of inter-domain DOTS deployment scenarios apply to intra-domain scenarios, it is expected that many externalities such as coordination of and authorization for routing advertisements and authoritative DNS updates may be automated to a higher degree than is practicable in inter-domain scenarios, given that the scope of required activities and authorizations are confined to a single organization. In theory, provisioning and change-control related both to DOTS itself as well as relevant externalities may require less administrative overhead and less implementation lead-times.

The scope of potential DDoS mitigation actions may also be broader in intra-organizational scenarios, as presumably an organization will have a higher degree of autonomy with regards to both techically and administratively feasible activities.

3.2.1. Suppression of outbound DDoS traffic originating from a consumer broadband access network

While most DDoS defenses concentrate on inbound DDoS attacks ingressing from direct peering links or upstream transit providers, the DDoS attack traffic in question originates from one or more Internet-connected networks. In some cases, compromised devices residing on the local networks of broadband access customers are used to directly generate this DDoS attack traffic; in others, misconfigured devices residing on said local customer networks are exploited by attackers to launch reflection/amplification DDoS attacks. In either scenario, the outbound DDoS traffic emanating from these devices can be just as disruptive as an inbound DDoS attack, and can cause disruption for substantial proportions of the broadband access network operator’s customer base.

Some broadband access network operators provide CPE devices (DSL modems/routers, cablemodems, FTTH routers, etc.) to their end- customers. Others allow end-customers to provide their own CPE devices. Many will either provide CPE devices or allow end-customers to supply their own.

Broadband access network operators typically have mechanisms to detect and classify both inbound and outbound DDoS attacks, utilizing flow telemetry exported from their peering/transit and customer aggregation routers. In the event of an outbound DDoS attack, they may make use of internally-developed systems which leverage their subscriber-management systems to de-provision end-customers who are sourcing outbound DDoS traffic; in some cases, they may have implemented quarantine systems to block all outbound traffic sourced



from the offending end-customers. In either case, the perceived disruption of the end-customer’s Internet access often prompts a help-desk call, which erodes the margins of the broadband access provider and can cause end-customer dissatisfaction.

Increasingly, CPE devices themselves are targeted by attackers who exploit security flaws in these devices in order to compromise them and subsume them into botnets, and then leverage them to launch outbound DDoS attacks. In all of the described scenarios, the end- customers are unaware that their computers and/or CPE devices have been compromised and are being used to launch outbound DDoS attacks - however, they may notice a degradation of their Internet connectivity as a result of outbound bandwidth consumption or other disruption.

By deploying DOTS-enabled telemetry systems and CPE devices (and possibly requiring DOTS functionality in customer-provided CPE devices), broadband access providers can utilize a standards-based mechanism to suppress outbound DDoS attack traffic while optionally allowing legitimate end-customer traffic to proceed unmolested.

In order to achieve this capability, the telemetry analysis system utilized by the broadband access provider must have DOTS client functionality, and the end-customer CPE devices must have DOTS server functionality. When the telemetry analysis system detects and classifies an outbound DDoS attack sourced from one or more end- customer networks/devices, the DOTS client of the telemetry analysis system sends a DOTS request to the DOTS server implemented on the CPE devices, requesting local mitigation assistance in suppressing either the identified outbound DDoS traffic, or all outbound traffic sourced from the end-customer networks/devices. The DOTS server residing within the CPE device(s) would then perform predefined actions such as implementing on-board access-control lists (ACLs) to suppress the outbound traffic in question and prevent it from leaving the local end-customer network(s).

Broadband access network operators may choose to implement a quarantine of all or selected network traffic originating from end- customer networks/devices which are sourcing outbound DDoS traffic, redirecting traffic from interactive applications such as Web browsers to an internal portal which informs the end-customer of the quarantine action, and providing instructions for self-remediation and/or helpdesk contact information.

Quarantine systems for broadband access networks are typically custom-developed and -maintained, and are generally deployed only by a relatively small number of broadband access providers with considerable internal software development and support capabilities. By requiring the manufacturers of operator-supplied CPE devices to



implement DOTS server functionality, and requiring customer-provided CPE devices to feature DOTS server functionality, broadband access network operators who previously could not afford the development expense of creating custom quarantine systems to integrate DOTS- enabled network telemetry systems to act as DOTS clients and perform effective quarantine of end-customer networks and devices until such time as they have been remediated.

3.2.2. Homenet DDoS Detection Collaboration for ISP network management

Home networks run with (limited) bandwidth as well as limited routing resources, while they are expected to provide services reachable from the outside [RFC7368]. This makes such networks some easy targets to DDoS attacks via their WAN interface. As these DDoS attacks are easy to perform, they may remain undetected by the upstream ISP. When the CPE is congested, the customer is likely to call the ISP hotline. In order to improve the quality of experience of the connectivity as well as to automate the request for DDoS mitigation, ISPs are likely to consider a standard mean for CPEs to automatically inform a dedicated service mitigation platform when they are under a suspected DDoS.

Note also that this section only considers DDoS attacks CPE or services in the home network are encountering. This differs from DDoS attacks the CPE or any device within the home network may take part of - such as botnets. In the later attacks, the home network generates traffic under the control of a botmaster. Such attacks may only be detected once the attacks have been characterized. It would be tempting to consider a feature in the DOTS protocol to allow a DOTS server to inform a CPE that some suspect traffic is being sent by the CPE so that appropriate actions are undertaken by the CPE/ user. Nevertheless, this feature would require some interaction with the CPE administrator. Such scenario is outside the scope of this document.

In this use case, ISPs are willing to prevent their customer undergoing DDoS attacks in order to enhance the quality of experience of their customers, to avoid unnecessary costly call on hot lines as well as to optimize the bandwidth of their network. A key challenge for the ISP is to detect DDoS attacks. In fact, DDoS detection is not only fine grained but is also expected to be different for each home network or small businesses networks (SOHO), and the ISP is unlikely to have sufficient resource to inspect the traffic of all its customers.

In order to address these challenges, ISPs are delegating the DDoS detection to CPE of home network or SOHO. Outsourcing the detection on the CPE provides the following advantages to the ISP: 1) Avoid the



ISP to dedicate a huge amount of resource for deep packet inspection over a large amount of traffic with a specific security policies associated to each home network. It is expected that such traffic only constitutes a small fraction of the total traffic the ISP is responsible for. 2) DDoS detection is deployed in a scalable way. 3) Provide more deterministic DDoS attack detection. For example, what could be suspected to be an UDP flood by the ISP may be consented by the terminating point hosted in the home network or SOHO. In fact, without specific home network security policies, the ISP is likely to detect DDoS attack over regular traffic or to miss DDoS attacks targeting a specific home network or CPE. In the first case, this would result in the ISP spending unnecessary resources and in the second case this would directly impact the quality of experience of the customer.

Note that in this scenario slightly differs from the "Enterprise with an upstream transit provider DDoS mitigation Service" scenario described in Section 3.1.1. In this scenario, the detection DDoS is motivated by the ISP in order to operate appropriately its network.

For that purpose, it requires some collaboration with the home network. In Section 3.1.1, the target network requests a mitigation service from the upstream transit provider in order to operate its services.

Even though the motivations differ, there are still significant advantages for the home network to collaborate. On the home network or SOHO perspective such collaboration provides the following advantages: 1) If it removes the flows contributing to a DDoS attacks, then it enhances the quality of experience of the users of the targeted services or the entire home network. 2) If mitigation is being handled by the ISP rather then the home network, then it reduces the management of DDoS attacks by the network administrator which involves detection as well as mitigation as well as the provisioning of extra resources. 3) If the DDoS detection is based on information specific to the home network, such as for example the description of the services, the hosts capacities or the network topology, then performing the DDoS detection by the home network instead of the ISP avoids the home network to leak private information to the ISP. In that sense, it better preserves the home network or SOHO privacy while enabling a better detection. However, the request for mitigation may still leak some informations. ISPs must not retrieve sensitive data without the consent of the user. This is usually captured in administrative contracts that are out of scope of this document.

When the CPE suspects an attack, it notifies automatically or the ISP. The contact address of the DDoS Mitigation service of the ISP



may be hard coded or may be configured manually or automatically (e.g., eventually the DHCP server may provide the DDoS mitigation service via specific DHCP options).

The communication to trigger a DDoS mitigation between the home network and the ISP is performed using DOTS. The home network CPE implements a DOTS client while the ISP implements a DOTS server.

The DOTS client on the CPE monitors the status of CPE’s resource and WAN link bandwidth usage. If something unusual happens based on preconfigured throughput, traffic patter, explicit action from the user, or some heuristics methods, the DOTS client sends a DOTS mitigation request to the ISP DOTS server. Typically, a default configuration with no additional information associated to the DOTS mitigation request is expected. The ISP derives traffic to mitigate from the CPE IP address.

In some cases, the DOTS mitigation request contains options such as some IP addresses or prefixes that belongs to a whitelist or a blacklist. In this case, the white and black lists are not associated to some analysis performed by the CPE - as the CPE is clearly not expected to analyze such attacks. Instead these are part of some configuration parameters. For example, in the case of small business, one may indicate specific legitimate IP addresses such as those used for VPNs, or third party services the company is likely to set a session. Similarly, the CPE may provide the IP addresses targeting the assets to be protected inside the network. Note that the IP address is the IP address used to reach the asset from the internet, and as such is expected to be globally routable. Such options may include the IP address as well as a service description. Similarly to the previous blacklist and whitelist, such information are likely not derived from a traffic analysis performed by the CPE, but instead are more related to configuration parameters.

Upon receiving the DOTS mitigation request, the DOTS server acknowledges its reception and confirms DDoS mitigation starts or not. Such feed back is mostly to avoid retransmission of the request.

Note that the ISP is connected to multiple CPEs and as such the CPE can potentially perform DDoS attack to the DOTS server. ISP may use gateways to absorbs the traffic. These gateways, will typically aggregate a smaller number of CPEs and retransmit to the destination DOTS Server a selected information. Note that such gateways may somehow act as a DOTS relay, which is implemented with a DOTS Server and a DOTS Client. Note also that the case of a large DDoS attack targeting simultaneously multiple CPEs is expected to be detected and



mitigated by the upstream architecture, eventually without DOTS alerts sent by each single CPE.

ISP may activate mitigation for the traffic associated to the CPE sending the alert or instead to the traffic associated to all CPE. Such decisions are not part of DOTS, but instead depend on the policies of the ISP.

It is unlikely the CPE will follow the status of the mitigation. The ISP is only expected to inform the CPE the mitigation has been stopped.

Upon receipt of such notification the CPE may, for example, re- activate the monitoring jobs and thus is likely to provide some further DOTS alert.

3.2.3. DDoS Orchestration

In this use case, one or multiple DDoS telemetry systems or monitoring devices like a flow collector monitor a network -- typically an ISP network. Upon detection of a DDoS attack, these telemetry systems alert an orchestrator in charge of coordinating the various DDoS mitigation systems within the domain. The telemetry systems may be configured to provide some necessary or useful pieces of information, such as a preliminary analysis of the observation to the orchestrator.

The orchestrator analyses the various information it receives from specialized equipement, and elaborates one or multiple DDoS mitigation strategies. In some case, a manual confirmation may also be required to choose a proposed strategy or to start the DDoS mitigation. The DDoS mitigation may consists in multiple steps such as configuring the network, the various hardware or already instantiated DDoS mitigation functions. In some cases, some specific virtual DDoS mitigation functions need to be instantiated and properly chained between each other. Eventually, the coordination of the mitigation may involve external DDoS resources such as a transit provider (Section 3.1.1) or an MSSP (Section 3.1.4).

The communication to trigger a DDoS mitigation between the telemetry and monitoring systems and the orchestrator is performed using DOTS. The telemetry systems implements a DOTS client while the Orchestrator implements a DOTS server.

The communication between a network administrator and the orchestrator is also performed using DOTS. The network administrator via its web interfaces implements a DOTS client, while the Orchestrator implements a DOTS server.



The communication between the Orchestrator and the DDoS mitigation systems is performed using DOTS. The Orchestrator implements a DOTS client while the DDoS mitigation systems implement a DOTS server.

The configuration aspects of each DDoS mitigation system, as well as the instantiations of DDoS mitigation functions or network configuration is not part of DOTS. Similarly, the discovery of available DDoS mitigation functions is not part of DOTS.

+----------+ | network |C | adminis |<-+ | trator | | +----------+ | | (internal) +----------+ | S+--------------+ +-----------+ |telemetry/| +->| |C S| DDoS |+ |monitoring|<--->| Orchestrator |<--->| mitigation|| |systems |C S| |<-+ | systems || +----------+ +--------------+C | +-----------+| | +----------+ | | (external) | +-----------+ | S| DDoS | +->| mitigation| | systems | +-----------+ * C is for DOTS client functionality * S is for DOTS server functionality

Figure 1: DDoS Orchestration

The telemetry systems monitor various traffic network and perform their measurement tasks. They are configured so that when an event or some measurements reach a predefined level to report a DOTS mitigation request to the Orchestrator. The DOTS mitigation request may be associated with some element such as specific reporting.

Upon receipt of the DOTS mitigation request from the telemetry system, the Orchestrator responds with an acknowledgement, to avoid retransmission of the request for mitigation. The status of the DDoS mitigation indicates the Orchestrator is in an analysing phase. The Orchestrator begins collecting various information from various telemetry systems in order to correlate the measurements and provide an analysis of the event. Eventually, the Orchestrator may ask



additional information to the telemetry system, however, the collection of these information is performed outside DOTS.

The Orchestrator may be configured to start a DDoS mitigation upon approval from a network administrator. The analysis from the orchestrator is reported to the network administrator via a web interface. If the network administrator decides to start the mitigation, she orders through her web interface a DOTS client to send a request for DDoS mitigation. This request is expected to be associated with a context that identifies the DDoS mitigation selected.

Upon receiving the DOTS request for DDoS mitigation from the network administrator, the orchestrator orchestrates the DDoS mitigation according to the specified strategy. Its status indicates the DDoS mitigation is starting while not effective.

Orchestration of the DDoS mitigation systems works similarly as described in Section 3.1.1 and Section 3.1.4. The Orchestrator indicates with its status whether the DDoS Mitigation is effective.

When the DDoS mitigation is finished on the DDoS mitigation systems, the orchestrator indicates to the Telemetry systems as well as to the network administrator the DDoS mitigation is finished.


DOTS is at risk from three primary attacks: DOTS agent impersonation, traffic injection, and signaling blocking. Associated security requirements and additional ones are defined in [I-D.ietf-dots-requirements].

Impersonation and traffic injection mitigation can be managed through current secure communications best practices. DOTS is not subject to anything new in this area. One consideration could be to minimize the security technologies in use at any one time. The more needed, the greater the risk of failures coming from assumptions on one technology providing protection that it does not in the presence of another technology.


No IANA considerations exist for this document at this time.



6. Acknowledgments

The authors would like to thank among others Tirumaleswar Reddy, , Andrew Mortensen, Mohamed Boucadaire, and the DOTS WG chairs Roman D. Danyliw and Tobias Gondrom for their valuable feed backs.

7. References




[I-D.ietf-dots-requirements] Mortensen, A., Moskowitz, R., and T. Reddy, "Distributed Denial of Service (DDoS) Open Threat Signaling Requirements", draft-ietf-dots-requirements-06 (work in progress), July 2017.

[I2NSF] "Interface to Network Security Functions (i2nsf)", n.d., <https://datatracker.ietf.org/wg/i2nsf/about/>.

[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. Cheshire, "Internet Assigned Numbers Authority (IANA) Procedures for the Management of the Service Name and Transport Protocol Port Number Registry", BCP 165, RFC 6335, DOI 10.17487/RFC6335, August 2011, <http://www.rfc-editor.org/info/rfc6335>.

[RFC7368] Chown, T., Ed., Arkko, J., Brandt, A., Troan, O., and J. Weil, "IPv6 Home Networking Architecture Principles", RFC 7368, DOI 10.17487/RFC7368, October 2014, <http://www.rfc-editor.org/info/rfc7368>.


Roland Dobbins Arbor Networks Singapore




Daniel Migault Ericsson 8400 boulevard Decarie Montreal, QC H4P 2N2 Canada


Stefan Fouant USA


Robert Moskowitz HTT Consulting Oak Park, MI 48237 USA


Nik Teague Verisign 12061 Bluemont Way Reston, VA 20190


Liang Xia Huawei No. 101, Software Avenue, Yuhuatai District Nanjing China





DOTS R. DobbinsInternet-Draft Arbor NetworksIntended status: Informational D. MigaultExpires: January 6, 2021 Ericsson R. Moskowitz HTT Consulting N. Teague Iron Mountain Data Centers L. Xia Huawei K. Nishizuka NTT Communications July 05, 2020

Use cases for DDoS Open Threat Signaling draft-ietf-dots-use-cases-25

Abstract

The DDoS Open Threat Signaling (DOTS) effort is intended to provide protocols to facilitate interoperability across disparate DDoS mitigation solutions. This document presents sample use cases which describe the interactions expected between the DOTS components as well as DOTS messaging exchanges. These use cases are meant to identify the interacting DOTS components, how they collaborate, and what are the typical information to be exchanged.

Status of This Memo







Copyright Notice



Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology and Acronyms . . . . . . . . . . . . . . . . . . 3 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Upstream DDoS Mitigation by an Upstream Internet Transit Provider . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2. DDoS Mitigation by a Third Party DDoS Mitigation Service Provider . . . . . . . . . . . . . . . . . . . . . . . . 7 3.3. DDoS Orchestration . . . . . . . . . . . . . . . . . . . 10 4. Security Considerations . . . . . . . . . . . . . . . . . . . 13 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 7. Informative References . . . . . . . . . . . . . . . . . . . 13 Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 14

1. Introduction

At the time of writing, distributed denial-of-service (DDoS) attack mitigation solutions are largely based upon siloed, proprietary communications schemes with vendor lock-in as a side-effect. This can result in the configuration, provisioning, operation, and activation of these solutions being a highly manual and often time- consuming process. Additionally, coordinating multiple DDoS mitigation solutions simultaneously is fraught with both technical and process-related hurdles. This greatly increases operational complexity which, in turn, can degrade the efficacy of mitigations that are generally highly dependent on a timely reaction by the system.

The DDoS Open Threat Signaling (DOTS) effort is intended to specify protocols that facilitate interoperability between diverse DDoS



mitigation solutions and ensure greater integration in term of attack detection, mitigation requests, and attack characterization patterns.

As DDoS solutions are broadly heterogeneous among vendors, the primary goal of DOTS is to provide high-level interaction amongst differing DDoS solutions, such as detecting DDoS attacks, initiating/ terminating DDoS mitigation assistance, or requesting the status of a DDoS mitigation.

This document provides sample use cases that provided input for the requirements [RFC8612] and design of the DOTS protocols [RFC8782][RFC8783]. The use cases are not exhaustive and future use cases are expected to emerge as DOTS is adopted and evolves.

2. Terminology and Acronyms

This document makes use of the same terminology and definitions as [RFC8612]. In addition it uses the terms defined below:

o DDoS Mitigation System (DMS): A system that performs DDoS mitigation. The DDoS Mitigation System may be composed of a cluster of hardware and/or software resources, but could also involve an orchestrator that may take decisions such as outsourcing some or all of the mitigation to another DDoS Mitigation System.

o DDoS Mitigation: The action performed by the DDoS Mitigation System.

o DDoS Mitigation Service: designates a service provided to a customer to mitigate DDoS attacks. Each service subscription usually involve Service Level Agreement (SLA) that has to be met. It is the responsibility of the DDoS Service provider to instantiate the DDoS Mitigation System to meet these SLAs.

o DDoS Mitigation Service Provider: designates the administrative entity providing the DDoS Mitigation Service.

o Internet Transit Provider (ITP): designates the entity that delivers the traffic to a customer network. It can be an Internet Service Provider (ISP), or an upstream entity delivering the traffic to the ISP.

3. Use Cases



3.1. Upstream DDoS Mitigation by an Upstream Internet Transit Provider

This use case describes how an enterprise or a residential customer network may take advantage of a pre-existing relation with its ITP in order to mitigate a DDoS attack targeting its network.

For clarity of discussion, the targeted network is indicated as an enterprise network, but the same scenario applies to any downstream network, including residential and cloud hosting networks.

As the ITP provides connectivity to the enterprise network, it is already on the path of the inbound and outbound traffic of the enterprise network and well aware of the networking parameters associated to the enterprise network WAN connectivity. This eases both the configuration and the instantiation of a DDoS Mitigation Service.

This section considers two kinds of DDoS Mitigation Service between an enterprise network and an ITP:

o The upstream ITP may instantiate a DDoS Mitigation System (DMS) upon receiving a request from the enterprise network. This typically corresponds to the case when the enterprise network is under attack.

o On the other hand, the ITP may identify an enterprise network as the source of an attack and send a mitigation request to the enterprise DMS to mitigate this at the source.

The two scenarios, though different, have similar interactions between the DOTS client and server. For the sake of simplicity, only the first scenario will be detailed in this section. Nevertheless, the second scenario is also in scope for DOTS.

In the first scenario, as depicted in Figure 1, an enterprise network with self-hosted Internet-facing properties such as Web servers, authoritative DNS servers, and VoIP servers has a DMS deployed to protect those servers and applications from DDoS attacks. In addition to on-premise DDoS defense capability, the enterprise has contracted with its ITP for DDoS Mitigation Services when attacks threaten to overwhelm the bandwidth of their WAN link(s).



+------------------+ +------------------+ | Enterprise | | Upstream | | Network | | Internet Transit | | | | Provider | | +--------+ | | DDoS Attack | | DDoS | | <================================= | | Target | | <================================= | +--------+ | | +------------+ | | | +-------->| DDoS | | | | | |S | Mitigation | | | | | | | System | | | | | | +------------+ | | | | | | | | | | | | | | | | | +------------+ | | | | | | DDoS |<---+ | | | | Mitigation |C | | | | | System | | | | | +------------+ | | | +------------------+ +------------------+

* C is for DOTS client functionality * S is for DOTS server functionality

Figure 1: Upstream Internet Transit Provider DDoS Mitigation

The enterprise DMS is configured such that if the incoming Internet traffic volume exceeds 50% of the provisioned upstream Internet WAN link capacity, the DMS will request DDoS mitigation assistance from the upstream transit provider. More sophisticated detection means may be considered as well.

The requests to trigger, manage, and finalize a DDoS Mitigation between the enterprise DMS and the ITP is performed using DOTS. The enterprise DMS implements a DOTS client while the ITP implements a DOTS server which is integrated with their DMS in this example.

When the enterprise DMS locally detects an inbound DDoS attack targeting its resources (e.g., servers, hosts, or applications), it immediately begins a DDoS Mitigation.

During the course of the attack, the inbound traffic volume to the enterprise network exceeds the 50% threshold and the enterprise DMS escalates the DDoS mitigation. The enterprise DMS DOTS client signals to the DOTS server on the upstream ITP to initiate DDoS Mitigation. The DOTS server replies to the DOTS client that it can



serve this request, and mitigation is initiated on the ITP network by the ITP DMS.

Over the course of the attack, the DOTS server of the ITP periodically informs the DOTS client on the mitigation status, statistics related to DDoS attack traffic mitigation, and related information. Once the DDoS attack has ended, or decreased to a certain level that the enterprise DMS might handle by itself, the DOTS server signals the enterprise DMS DOTS client that the attack has subsided.

The DOTS client on the enterprise DMS then requests the ITP to terminate the DDoS Mitigation. The DOTS server on the ITP receives this request and once the mitigation has ended, confirms the end of upstream DDoS Mitigation to the enterprise DMS DOTS client.

The following is an overview of the DOTS communication model for this use-case:

1. A DDoS attack is initiated against resources of a network organization (here, the enterprise) which has deployed a DOTS- capable DMS - typically a DOTS client.

2. The enterprise DMS detects, classifies, and begins the DDoS Mitigation.

3. The enterprise DMS determines that its capacity and/or capability to mitigate the DDoS attack is insufficient, and sends via its DOTS client a DOTS DDoS Mitigation request to one or more DOTS servers residing on the upstream ITP.

4. The DOTS server which receives the DOTS Mitigation request determines that it has been configured to honor requests from the requesting DOTS client, and honors the request by orchestrating its own DMS.

5. While the DDoS Mitigation is active, the DOTS server regularly transmits DOTS DDoS Mitigation status updates to the DOTS client.

6. Informed by the DOTS server status update that the attack has ended or subsided, the DOTS client transmits a DOTS DDoS Mitigation termination request to the DOTS server.

7. The DOTS server terminates DDoS Mitigation, and sends the notification to the DOTS client.

Note that communications between the enterprise DOTS client and the upstream ITP DOTS server may take place in-band within the main



Internet WAN link between the enterprise and the ITP; out-of-band via a separate, dedicated wireline network link utilized solely for DOTS signaling; or out-of-band via some other form of network connectivity such as a third-party wireless 4G network connectivity.

Note also that a DOTS client that sends a DOTS Mitigation request may be also triggered by a network admin that manually confirms the request to the upstream ITP, in which case the request may be sent from an application such as a web browser or a dedicated mobile application.

Note also that when the enterprise is multihomed and connected to multiple upstream ITPs, each ITP is only able to provide a DDoS Mitigation Service for the traffic it transits. As a result, the enterprise network may be required to coordinate the various DDoS Mitigation Services associated to each link. More multi-homing considerations are discussed in [I-D.ietf-dots-multihoming].

3.2. DDoS Mitigation by a Third Party DDoS Mitigation Service Provider

This use case differs from the previous use case described in Section 3.1 in that the DDoS Mitigation Service is not provided by an upstream ITP. In other words, as represented in Figure 2, the traffic is not forwarded through the DDoS Mitigation Service Provider by default. In order to steer the traffic to the DDoS Mitigation Service Provider, some network configuration changes are required. As such, this use case is likely to apply to large enterprises or large data centers, but as for the other use cases is not exclusively limited to them.

Another typical scenario for this use case is for there to be a relationship between DDoS Mitigation Service Providers, forming an overlay of DMS. When a DDoS Mitigation Service Provider mitigating a DDoS attack reaches its resources capacity, it may chose to delegate the DDoS Mitigation to another DDoS Mitigation Service Provider.



+------------------+ +------------------+ | Enterprise | | Upstream | | Network | | Internet Transit | | | | Provider | | +--------+ | | DDoS Attack | | DDoS | | <================================= | | Target | | <================================= | +--------+ | | | | | | | | | +------------------+ | | | | +------------------+ | | | DDoS Mitigation | | | | Service Provider | | | | | | +------------+ | | +------------+ | | | DDoS |<------------>| DDoS | | | | Mitigation |C | | S| Mitigation | | | | System | | | | System | | | +------------+ | | +------------+ | +------------------+ +------------------+


Figure 2: DDoS Mitigation between an Enterprise Network and Third Party DDoS Mitigation Service Provider

In this scenario, an enterprise network has entered into a pre- arranged DDoS mitigation assistance agreement with one or more third- party DDoS Mitigation Service Providers in order to ensure that sufficient DDoS mitigation capacity and/or capabilities may be activated in the event that a given DDoS attack threatens to overwhelm the ability of the enterprise’s or any other given DMS to mitigate the attack on its own.

The pre-arrangement typically includes agreement on the mechanisms used to redirect the traffic to the DDoS Mitigation Service Provider, as well as the mechanism to re-inject the traffic back to the Enterprise Network. Redirection to the DDoS Mitigation Service Provider typically involves BGP prefix announcement or DNS redirection, while re-injection of the scrubbed traffic to the enterprise network may be performed via tunneling mechanisms (e.g., GRE). The exact mechanisms used for traffic steering are out of scope of DOTS, but will need to be pre-arranged, while in some contexts such changes could be detected and considered as an attack.



In some cases the communication between the enterprise DOTS client and the DOTS server of the DDoS Mitigation Service Provider may go through the ITP carrying the DDoS attack, which would affect the communication. On the other hand, the communication between the DOTS client and DOTS server may take a path that is not undergoing a DDoS attack.

+------------------+ +------------------+ | Enterprise | | Upstream | | Network | | Internet Transit | | | | Provider | | +--------+ | | DDoS Attack | | DDoS | |<----------------+ | ++==== | | Target | | Mitigated | | || ++= | +--------+ | | | | || || | | | | | || || | | +--------|---------+ || || | | | || || | | +--------|---------+ || || | | | DDoS Mitigation | || || | | | Service Provider | || || | | | | | || || | +------------+ | | +------------+ | || || | | DDoS |<------------>| DDoS | | || || | | mitigation |C | |S | mitigation |<===++ || | | system | | | | system |<======++ | +------------+ | | +------------+ | +------------------+ +------------------+


Figure 3: Redirection to a DDoS Mitigation Service Provider

When the enterprise network is under attack or at least is reaching its capacity or ability to mitigate a given DDoS attack, the DOTS client sends a DOTS request to the DDoS Mitigation Service Provider to initiate network traffic diversion - as represented in Figure 3 - and DDoS mitigation activities. Ongoing attack and mitigation status messages may be passed between the enterprise network and the DDoS Mitigation Service Provider using DOTS. If the DDoS attack has stopped or the severity of the attack has subsided, the DOTS client can request the DDoS Mitigation Service Provider to terminate the DDoS Mitigation.



3.3. DDoS Orchestration

In this use case, one or more DDoS telemetry systems or monitoring devices monitor a network - typically an ISP network, an enterprise network, or a data center. Upon detection of a DDoS attack, these DDoS telemetry systems alert an orchestrator in charge of coordinating the various DMS’s within the domain. The DDoS telemetry systems may be configured to provide required information, such as a preliminary analysis of the observation, to the orchestrator.

The orchestrator analyses the various sets of information it receives from DDoS telemetry systems, and initiates one or more DDoS mitigation strategies. For example, the orchestrator could select the DDoS mitigation system in the enterprise network or one provided by the ITP.

DDoS Mitigation System selection and DDoS Mitigation techniques may depend on the type of the DDoS attack. In some case, a manual confirmation or selection may also be required to choose a proposed strategy to initiate a DDoS Mitigation. The DDoS Mitigation may consist of multiple steps such as configuring the network, or of updating already instantiated DDoS mitigation functions. Eventually, the coordination of the mitigation may involve external DDoS mitigation resources such as a transit provider or a Third Party DDoS Mitigation Service Provider.

The communication used to trigger a DDoS Mitigation between the DDoS telemetry and monitoring systems and the orchestrator is performed using DOTS. The DDoS telemetry system implements a DOTS client while the orchestrator implements a DOTS server.

The communication between a network administrator and the orchestrator is also performed using DOTS. The network administrator uses, for example, a web interface which interacts with a DOTS client, while the orchestrator implements a DOTS server.

The communication between the orchestrator and the DDoS Mitigation Systems is performed using DOTS. The orchestrator implements a DOTS client while the DDoS Mitigation Systems implement a DOTS server.

The configuration aspects of each DDoS Mitigation System, as well as the instantiations of DDoS mitigation functions or network configuration is not part of DOTS. Similarly, the discovery of available DDoS mitigation functions is not part of DOTS; and as such is out of scope.



+----------+ | network |C (Enterprise Network) | adminis |<-+ | trator | | +----------+ | | +----------+ | S+--------------+ +-----------+ |telemetry/| +->| |C S| DDoS |+ |monitoring|<--->| Orchestrator |<--->| mitigation|| |systems |C S| |<-+ | systems || +----------+ +--------------+C | +-----------+| | +----------+ -----------------------------------|----------------- | | (Internet Transit Provider) | | +-----------+ | S| DDoS |+ +->| mitigation|| | systems || +-----------+| * C is for DOTS client functionality +----------+ * S is for DOTS server functionality

Figure 4: DDoS Orchestration

The DDoS telemetry systems monitor various aspects of the network traffic and perform some measurement tasks.

These systems are configured so that when an event or some measurement indicators reach a predefined level their associated DOTS client sends a DOTS mitigation request to the orchestrator DOTS server. The DOTS mitigation request may be associated with some optional mitigation hints to let the orchestrator know what has triggered the request. In particular, it is possible for something that locally to one telemetry system looks like an attack is not actually an attack when seen from the broader scope (e.g., of the orchestrator)

Upon receipt of the DOTS mitigation request from the DDoS telemetry system, the orchestrator DOTS server responds with an acknowledgment, to avoid retransmission of the request for mitigation. The orchestrator may begin collecting additional fine-grained and specific information from various DDoS telemetry systems in order to correlate the measurements and provide an analysis of the event. Eventually, the orchestrator may ask for additional information from the DDoS telemetry system; however, the collection of this information is out of scope of DOTS.



The orchestrator may be configured to start a DDoS Mitigation upon approval from a network administrator. The analysis from the orchestrator is reported to the network administrator via, for example, a web interface. If the network administrator decides to start the mitigation, the network administrator triggers the DDoS mitigation request using, for example, a web interface of a DOTS client communicating to the orchestrator DOTS server. This request is expected to be associated with a context that provides sufficient information to the orchestrator DOTS server to infer, elaborate and coordinate the appropriate DDoS Mitigation.

Upon receiving a request to mitigate a DDoS attack aimed at a target, the orchestrator may evaluate the volume of the attack as well as the value that the target represents. The orchestrator may select the DDoS Mitigation Service Provider based on the attack severity. It may also coordinate the DDoS Mitigation performed by the DDoS Mitigation Service Provider with some other tasks such as, for example, moving the target to another network so new sessions will not be impacted. The orchestrator requests a DDoS Mitigation by the selected DDoS mitigation systems via its DOTS client, as described in Section 3.1.

The orchestrator DOTS client is notified that the DDoS Mitigation is effective by the selected DDoS mitigation systems. The orchestrator DOTS server returns this information back to the network administrator.

Similarly, when the DDoS attack has stopped, the orchestrator DOTS client is notified and the orchestrator’s DOTS server indicates to the DDoS telemetry systems as well as to the network administrator the end of the DDoS Mitigation.

In addition to the above DDoS Orchestration, the selected DDoS mitigation system can return back a mitigation request to the orchestrator as an offloading. For example, when the DDoS attack becomes severe and the DDoS mitigation system’s utilization rate reaches its maximum capacity, the DDoS mitigation system can send mitigation requests with additional hints such as its blocked traffic information to the orchestrator. Then the orchestrator can take further actions such as requesting forwarding nodes such as routers to filter the traffic. In this case, the DDoS mitigation system implements a DOTS client while the orchestrator implements a DOTS server. Similar to other DOTS use cases, the offloading scenario assumes that some validation checks are followed by the DMS, the orchestrator, or both (e.g., avoid exhausting the resources of the forwarding nodes or inadvertent disruption of legitimate services). These validation checks are part of the mitigation, and are therefore out of the scope of the document.




The document does not describe any protocol, though there are still a few high-level security considerations to discuss.

DOTS is at risk from three primary attacks: DOTS agent impersonation, traffic injection, and signaling blocking.

Impersonation and traffic injection mitigation can be mitigated through current secure communications best practices including mutual authentication. Preconfigured mitigation steps to take on the loss of keepalive traffic can partially mitigate signal blocking, but in general it is impossible to comprehensively defend against an attacker that can selectively block any or all traffic. Alternate communication paths that are (hopefully) not subject to blocking by the attacker in question is another potential mitigation.

Additional details of DOTS security requirements can be found in [RFC8612].

Service disruption may be experienced if inadequate mitigation actions are applied. These considerations are out of the scope of DOTS.


No IANA considerations exist for this document.

6. Acknowledgments

The authors would like to thank among others Tirumaleswar Reddy; Andrew Mortensen; Mohamed Boucadair; Artyom Gavrichenkov; Jon Shallow, Yuuhei Hayashi, Elwyn Davies, the DOTS WG chairs, Roman Danyliw and Tobias Gondrom as well as the Security AD Benjamin Kaduk for their valuable feedback.

We also would like to thank Stephan Fouant that was part of the initial co-authors of the documents.

7. Informative References

[I-D.ietf-dots-multihoming] Boucadair, M., Reddy.K, T., and W. Pan, "Multi-homing Deployment Considerations for Distributed-Denial-of- Service Open Threat Signaling (DOTS)", draft-ietf-dots- multihoming-04 (work in progress), May 2020.




[RFC8782] Reddy.K, T., Ed., Boucadair, M., Ed., Patil, P., Mortensen, A., and N. Teague, "Distributed Denial-of- Service Open Threat Signaling (DOTS) Signal Channel Specification", RFC 8782, DOI 10.17487/RFC8782, May 2020, <https://www.rfc-editor.org/info/rfc8782>.

[RFC8783] Boucadair, M., Ed. and T. Reddy.K, Ed., "Distributed Denial-of-Service Open Threat Signaling (DOTS) Data Channel Specification", RFC 8783, DOI 10.17487/RFC8783, May 2020, <https://www.rfc-editor.org/info/rfc8783>.


Roland Dobbins Arbor Networks Singapore


Daniel Migault Ericsson 8275 Trans Canada Route Saint Laurent, QC 4S 0B6 Canada


Robert Moskowitz HTT Consulting Oak Park, MI 48237 USA


Nik Teague Iron Mountain Data Centers UK




Liang Xia Huawei No. 101, Software Avenue, Yuhuatai District Nanjing China



